The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/cam/cam_iosched.c

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    1 /*-
    2  * CAM IO Scheduler Interface
    3  *
    4  * Copyright (c) 2015 Netflix, Inc.
    5  * All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice, this list of conditions, and the following disclaimer,
   12  *    without modification, immediately at the beginning of the file.
   13  * 2. The name of the author may not be used to endorse or promote products
   14  *    derived from this software without specific prior written permission.
   15  *
   16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   19  * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
   20  * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   26  * SUCH DAMAGE.
   27  *
   28  * $FreeBSD: releng/11.0/sys/cam/cam_iosched.c 302396 2016-07-07 20:31:35Z imp $
   29  */
   30 
   31 #include "opt_cam.h"
   32 #include "opt_ddb.h"
   33 
   34 #include <sys/cdefs.h>
   35 __FBSDID("$FreeBSD: releng/11.0/sys/cam/cam_iosched.c 302396 2016-07-07 20:31:35Z imp $");
   36 
   37 #include <sys/param.h>
   38 
   39 #include <sys/systm.h>
   40 #include <sys/kernel.h>
   41 #include <sys/bio.h>
   42 #include <sys/lock.h>
   43 #include <sys/malloc.h>
   44 #include <sys/mutex.h>
   45 #include <sys/sysctl.h>
   46 
   47 #include <cam/cam.h>
   48 #include <cam/cam_ccb.h>
   49 #include <cam/cam_periph.h>
   50 #include <cam/cam_xpt_periph.h>
   51 #include <cam/cam_iosched.h>
   52 
   53 #include <ddb/ddb.h>
   54 
   55 static MALLOC_DEFINE(M_CAMSCHED, "CAM I/O Scheduler",
   56     "CAM I/O Scheduler buffers");
   57 
   58 /*
   59  * Default I/O scheduler for FreeBSD. This implementation is just a thin-vineer
   60  * over the bioq_* interface, with notions of separate calls for normal I/O and
   61  * for trims.
   62  *
   63  * When CAM_IOSCHED_DYNAMIC is defined, the scheduler is enhanced to dynamically
   64  * steer the rate of one type of traffic to help other types of traffic (eg
   65  * limit writes when read latency deteriorates on SSDs).
   66  */
   67 
   68 #ifdef CAM_IOSCHED_DYNAMIC
   69 
   70 static int do_dynamic_iosched = 1;
   71 TUNABLE_INT("kern.cam.do_dynamic_iosched", &do_dynamic_iosched);
   72 SYSCTL_INT(_kern_cam, OID_AUTO, do_dynamic_iosched, CTLFLAG_RD,
   73     &do_dynamic_iosched, 1,
   74     "Enable Dynamic I/O scheduler optimizations.");
   75 
   76 static int alpha_bits = 9;
   77 TUNABLE_INT("kern.cam.iosched_alpha_bits", &alpha_bits);
   78 SYSCTL_INT(_kern_cam, OID_AUTO, iosched_alpha_bits, CTLFLAG_RW,
   79     &alpha_bits, 1,
   80     "Bits in EMA's alpha.");
   81 
   82 
   83 
   84 struct iop_stats;
   85 struct cam_iosched_softc;
   86 
   87 int iosched_debug = 0;
   88 
   89 typedef enum {
   90         none = 0,                               /* No limits */
   91         queue_depth,                    /* Limit how many ops we queue to SIM */
   92         iops,                           /* Limit # of IOPS to the drive */
   93         bandwidth,                      /* Limit bandwidth to the drive */
   94         limiter_max
   95 } io_limiter;
   96         
   97 static const char *cam_iosched_limiter_names[] =
   98     { "none", "queue_depth", "iops", "bandwidth" };
   99 
  100 /*
  101  * Called to initialize the bits of the iop_stats structure relevant to the
  102  * limiter. Called just after the limiter is set.
  103  */
  104 typedef int l_init_t(struct iop_stats *);
  105 
  106 /*
  107  * Called every tick.
  108  */
  109 typedef int l_tick_t(struct iop_stats *);
  110 
  111 /*
  112  * Called to see if the limiter thinks this IOP can be allowed to
  113  * proceed. If so, the limiter assumes that the while IOP proceeded
  114  * and makes any accounting of it that's needed.
  115  */ 
  116 typedef int l_iop_t(struct iop_stats *, struct bio *);
  117 
  118 /*
  119  * Called when an I/O completes so the limiter can updates its
  120  * accounting. Pending I/Os may complete in any order (even when
  121  * sent to the hardware at the same time), so the limiter may not
  122  * make any assumptions other than this I/O has completed. If it
  123  * returns 1, then xpt_schedule() needs to be called again.
  124  */
  125 typedef int l_iodone_t(struct iop_stats *, struct bio *);
  126 
  127 static l_iop_t cam_iosched_qd_iop;
  128 static l_iop_t cam_iosched_qd_caniop;
  129 static l_iodone_t cam_iosched_qd_iodone;
  130 
  131 static l_init_t cam_iosched_iops_init;
  132 static l_tick_t cam_iosched_iops_tick;
  133 static l_iop_t cam_iosched_iops_caniop;
  134 static l_iop_t cam_iosched_iops_iop;
  135 
  136 static l_init_t cam_iosched_bw_init;
  137 static l_tick_t cam_iosched_bw_tick;
  138 static l_iop_t cam_iosched_bw_caniop;
  139 static l_iop_t cam_iosched_bw_iop;
  140 
  141 struct limswitch 
  142 {
  143         l_init_t        *l_init;
  144         l_tick_t        *l_tick;
  145         l_iop_t         *l_iop;
  146         l_iop_t         *l_caniop;
  147         l_iodone_t      *l_iodone;
  148 } limsw[] =
  149 {
  150         {       /* none */
  151                 .l_init = NULL,
  152                 .l_tick = NULL,
  153                 .l_iop = NULL,
  154                 .l_iodone= NULL,
  155         },
  156         {       /* queue_depth */
  157                 .l_init = NULL,
  158                 .l_tick = NULL,
  159                 .l_caniop = cam_iosched_qd_caniop,
  160                 .l_iop = cam_iosched_qd_iop,
  161                 .l_iodone= cam_iosched_qd_iodone,
  162         },
  163         {       /* iops */
  164                 .l_init = cam_iosched_iops_init,
  165                 .l_tick = cam_iosched_iops_tick,
  166                 .l_caniop = cam_iosched_iops_caniop,
  167                 .l_iop = cam_iosched_iops_iop,
  168                 .l_iodone= NULL,
  169         },
  170         {       /* bandwidth */
  171                 .l_init = cam_iosched_bw_init,
  172                 .l_tick = cam_iosched_bw_tick,
  173                 .l_caniop = cam_iosched_bw_caniop,
  174                 .l_iop = cam_iosched_bw_iop,
  175                 .l_iodone= NULL,
  176         },
  177 };
  178 
  179 struct iop_stats 
  180 {
  181         /*
  182          * sysctl state for this subnode.
  183          */
  184         struct sysctl_ctx_list  sysctl_ctx;
  185         struct sysctl_oid       *sysctl_tree;
  186 
  187         /*
  188          * Information about the current rate limiters, if any
  189          */
  190         io_limiter      limiter;        /* How are I/Os being limited */
  191         int             min;            /* Low range of limit */
  192         int             max;            /* High range of limit */
  193         int             current;        /* Current rate limiter */
  194         int             l_value1;       /* per-limiter scratch value 1. */
  195         int             l_value2;       /* per-limiter scratch value 2. */
  196         
  197 
  198         /*
  199          * Debug information about counts of I/Os that have gone through the
  200          * scheduler.
  201          */
  202         int             pending;        /* I/Os pending in the hardware */
  203         int             queued;         /* number currently in the queue */
  204         int             total;          /* Total for all time -- wraps */
  205         int             in;             /* number queued all time -- wraps */
  206         int             out;            /* number completed all time -- wraps */
  207         
  208         /*
  209          * Statistics on different bits of the process.
  210          */
  211                 /* Exp Moving Average, alpha = 1 / (1 << alpha_bits) */
  212         sbintime_t      ema;
  213         sbintime_t      emss;           /* Exp Moving sum of the squares */
  214         sbintime_t      sd;             /* Last computed sd */
  215 
  216         struct cam_iosched_softc *softc;
  217 };
  218 
  219 
  220 typedef enum {
  221         set_max = 0,                    /* current = max */
  222         read_latency,                   /* Steer read latency by throttling writes */
  223         cl_max                          /* Keep last */
  224 } control_type;
  225 
  226 static const char *cam_iosched_control_type_names[] =
  227     { "set_max", "read_latency" };
  228 
  229 struct control_loop
  230 {
  231         /*
  232          * sysctl state for this subnode.
  233          */
  234         struct sysctl_ctx_list  sysctl_ctx;
  235         struct sysctl_oid       *sysctl_tree;
  236 
  237         sbintime_t      next_steer;             /* Time of next steer */
  238         sbintime_t      steer_interval;         /* How often do we steer? */
  239         sbintime_t      lolat;
  240         sbintime_t      hilat;
  241         int             alpha;
  242         control_type    type;                   /* What type of control? */
  243         int             last_count;             /* Last I/O count */
  244 
  245         struct cam_iosched_softc *softc;
  246 };
  247 
  248 #endif
  249 
  250 struct cam_iosched_softc
  251 {
  252         struct bio_queue_head bio_queue;
  253         struct bio_queue_head trim_queue;
  254                                 /* scheduler flags < 16, user flags >= 16 */
  255         uint32_t        flags;
  256         int             sort_io_queue;
  257 #ifdef CAM_IOSCHED_DYNAMIC
  258         int             read_bias;              /* Read bias setting */
  259         int             current_read_bias;      /* Current read bias state */
  260         int             total_ticks;
  261 
  262         struct bio_queue_head write_queue;
  263         struct iop_stats read_stats, write_stats, trim_stats;
  264         struct sysctl_ctx_list  sysctl_ctx;
  265         struct sysctl_oid       *sysctl_tree;
  266 
  267         int             quanta;                 /* Number of quanta per second */
  268         struct callout  ticker;                 /* Callout for our quota system */
  269         struct cam_periph *periph;              /* cam periph associated with this device */
  270         uint32_t        this_frac;              /* Fraction of a second (1024ths) for this tick */
  271         sbintime_t      last_time;              /* Last time we ticked */
  272         struct control_loop cl;
  273 #endif
  274 };
  275 
  276 #ifdef CAM_IOSCHED_DYNAMIC
  277 /*
  278  * helper functions to call the limsw functions.
  279  */
  280 static int
  281 cam_iosched_limiter_init(struct iop_stats *ios)
  282 {
  283         int lim = ios->limiter;
  284 
  285         /* maybe this should be a kassert */
  286         if (lim < none || lim >= limiter_max)
  287                 return EINVAL;
  288 
  289         if (limsw[lim].l_init)
  290                 return limsw[lim].l_init(ios);
  291 
  292         return 0;
  293 }
  294 
  295 static int
  296 cam_iosched_limiter_tick(struct iop_stats *ios)
  297 {
  298         int lim = ios->limiter;
  299 
  300         /* maybe this should be a kassert */
  301         if (lim < none || lim >= limiter_max)
  302                 return EINVAL;
  303 
  304         if (limsw[lim].l_tick)
  305                 return limsw[lim].l_tick(ios);
  306 
  307         return 0;
  308 }
  309 
  310 static int
  311 cam_iosched_limiter_iop(struct iop_stats *ios, struct bio *bp)
  312 {
  313         int lim = ios->limiter;
  314 
  315         /* maybe this should be a kassert */
  316         if (lim < none || lim >= limiter_max)
  317                 return EINVAL;
  318 
  319         if (limsw[lim].l_iop)
  320                 return limsw[lim].l_iop(ios, bp);
  321 
  322         return 0;
  323 }
  324 
  325 static int
  326 cam_iosched_limiter_caniop(struct iop_stats *ios, struct bio *bp)
  327 {
  328         int lim = ios->limiter;
  329 
  330         /* maybe this should be a kassert */
  331         if (lim < none || lim >= limiter_max)
  332                 return EINVAL;
  333 
  334         if (limsw[lim].l_caniop)
  335                 return limsw[lim].l_caniop(ios, bp);
  336 
  337         return 0;
  338 }
  339 
  340 static int
  341 cam_iosched_limiter_iodone(struct iop_stats *ios, struct bio *bp)
  342 {
  343         int lim = ios->limiter;
  344 
  345         /* maybe this should be a kassert */
  346         if (lim < none || lim >= limiter_max)
  347                 return 0;
  348 
  349         if (limsw[lim].l_iodone)
  350                 return limsw[lim].l_iodone(ios, bp);
  351 
  352         return 0;
  353 }
  354 
  355 /*
  356  * Functions to implement the different kinds of limiters
  357  */
  358 
  359 static int
  360 cam_iosched_qd_iop(struct iop_stats *ios, struct bio *bp)
  361 {
  362                 
  363         if (ios->current <= 0 || ios->pending < ios->current)
  364                 return 0;
  365 
  366         return EAGAIN;
  367 }
  368 
  369 static int
  370 cam_iosched_qd_caniop(struct iop_stats *ios, struct bio *bp)
  371 {
  372                 
  373         if (ios->current <= 0 || ios->pending < ios->current)
  374                 return 0;
  375 
  376         return EAGAIN;
  377 }
  378 
  379 static int
  380 cam_iosched_qd_iodone(struct iop_stats *ios, struct bio *bp)
  381 {
  382                 
  383         if (ios->current <= 0 || ios->pending != ios->current)
  384                 return 0;
  385 
  386         return 1;
  387 }
  388 
  389 static int
  390 cam_iosched_iops_init(struct iop_stats *ios)
  391 {
  392 
  393         ios->l_value1 = ios->current / ios->softc->quanta;
  394         if (ios->l_value1 <= 0)
  395                 ios->l_value1 = 1;
  396 
  397         return 0;
  398 }
  399 
  400 static int
  401 cam_iosched_iops_tick(struct iop_stats *ios)
  402 {
  403 
  404         ios->l_value1 = (int)((ios->current * (uint64_t)ios->softc->this_frac) >> 16);
  405         if (ios->l_value1 <= 0)
  406                 ios->l_value1 = 1;
  407 
  408         return 0;
  409 }
  410 
  411 static int
  412 cam_iosched_iops_caniop(struct iop_stats *ios, struct bio *bp)
  413 {
  414 
  415         /*
  416          * So if we have any more IOPs left, allow it,
  417          * otherwise wait.
  418          */
  419         if (ios->l_value1 <= 0)
  420                 return EAGAIN;
  421         return 0;
  422 }
  423 
  424 static int
  425 cam_iosched_iops_iop(struct iop_stats *ios, struct bio *bp)
  426 {
  427         int rv;
  428 
  429         rv = cam_iosched_limiter_caniop(ios, bp);
  430         if (rv == 0)
  431                 ios->l_value1--;
  432 
  433         return rv;
  434 }
  435 
  436 static int
  437 cam_iosched_bw_init(struct iop_stats *ios)
  438 {
  439 
  440         /* ios->current is in kB/s, so scale to bytes */
  441         ios->l_value1 = ios->current * 1000 / ios->softc->quanta;
  442 
  443         return 0;
  444 }
  445 
  446 static int
  447 cam_iosched_bw_tick(struct iop_stats *ios)
  448 {
  449         int bw;
  450 
  451         /*
  452          * If we're in the hole for available quota from
  453          * the last time, then add the quantum for this.
  454          * If we have any left over from last quantum,
  455          * then too bad, that's lost. Also, ios->current
  456          * is in kB/s, so scale.
  457          *
  458          * We also allow up to 4 quanta of credits to
  459          * accumulate to deal with burstiness. 4 is extremely
  460          * arbitrary.
  461          */
  462         bw = (int)((ios->current * 1000ull * (uint64_t)ios->softc->this_frac) >> 16);
  463         if (ios->l_value1 < bw * 4)
  464                 ios->l_value1 += bw;
  465 
  466         return 0;
  467 }
  468 
  469 static int
  470 cam_iosched_bw_caniop(struct iop_stats *ios, struct bio *bp)
  471 {
  472         /*
  473          * So if we have any more bw quota left, allow it,
  474          * otherwise wait. Not, we'll go negative and that's
  475          * OK. We'll just get a lettle less next quota.
  476          *
  477          * Note on going negative: that allows us to process
  478          * requests in order better, since we won't allow
  479          * shorter reads to get around the long one that we
  480          * don't have the quota to do just yet. It also prevents
  481          * starvation by being a little more permissive about
  482          * what we let through this quantum (to prevent the
  483          * starvation), at the cost of getting a little less
  484          * next quantum.
  485          */
  486         if (ios->l_value1 <= 0)
  487                 return EAGAIN;
  488 
  489 
  490         return 0;
  491 }
  492 
  493 static int
  494 cam_iosched_bw_iop(struct iop_stats *ios, struct bio *bp)
  495 {
  496         int rv;
  497 
  498         rv = cam_iosched_limiter_caniop(ios, bp);
  499         if (rv == 0)
  500                 ios->l_value1 -= bp->bio_length;
  501 
  502         return rv;
  503 }
  504 
  505 static void cam_iosched_cl_maybe_steer(struct control_loop *clp);
  506 
  507 static void
  508 cam_iosched_ticker(void *arg)
  509 {
  510         struct cam_iosched_softc *isc = arg;
  511         sbintime_t now, delta;
  512 
  513         callout_reset(&isc->ticker, hz / isc->quanta - 1, cam_iosched_ticker, isc);
  514 
  515         now = sbinuptime();
  516         delta = now - isc->last_time;
  517         isc->this_frac = (uint32_t)delta >> 16;         /* Note: discards seconds -- should be 0 harmless if not */
  518         isc->last_time = now;
  519 
  520         cam_iosched_cl_maybe_steer(&isc->cl);
  521 
  522         cam_iosched_limiter_tick(&isc->read_stats);
  523         cam_iosched_limiter_tick(&isc->write_stats);
  524         cam_iosched_limiter_tick(&isc->trim_stats);
  525 
  526         cam_iosched_schedule(isc, isc->periph);
  527 
  528         isc->total_ticks++;
  529 }
  530 
  531 
  532 static void
  533 cam_iosched_cl_init(struct control_loop *clp, struct cam_iosched_softc *isc)
  534 {
  535 
  536         clp->next_steer = sbinuptime();
  537         clp->softc = isc;
  538         clp->steer_interval = SBT_1S * 5;       /* Let's start out steering every 5s */
  539         clp->lolat = 5 * SBT_1MS;
  540         clp->hilat = 15 * SBT_1MS;
  541         clp->alpha = 20;                        /* Alpha == gain. 20 = .2 */
  542         clp->type = set_max;
  543 }
  544 
  545 static void
  546 cam_iosched_cl_maybe_steer(struct control_loop *clp)
  547 {
  548         struct cam_iosched_softc *isc;
  549         sbintime_t now, lat;
  550         int old;
  551 
  552         isc = clp->softc;
  553         now = isc->last_time;
  554         if (now < clp->next_steer)
  555                 return;
  556 
  557         clp->next_steer = now + clp->steer_interval;
  558         switch (clp->type) {
  559         case set_max:
  560                 if (isc->write_stats.current != isc->write_stats.max)
  561                         printf("Steering write from %d kBps to %d kBps\n",
  562                             isc->write_stats.current, isc->write_stats.max);
  563                 isc->read_stats.current = isc->read_stats.max;
  564                 isc->write_stats.current = isc->write_stats.max;
  565                 isc->trim_stats.current = isc->trim_stats.max;
  566                 break;
  567         case read_latency:
  568                 old = isc->write_stats.current;
  569                 lat = isc->read_stats.ema;
  570                 /*
  571                  * Simple PLL-like engine. Since we're steering to a range for
  572                  * the SP (set point) that makes things a little more
  573                  * complicated. In addition, we're not directly controlling our
  574                  * PV (process variable), the read latency, but instead are
  575                  * manipulating the write bandwidth limit for our MV
  576                  * (manipulation variable), analysis of this code gets a bit
  577                  * messy. Also, the MV is a very noisy control surface for read
  578                  * latency since it is affected by many hidden processes inside
  579                  * the device which change how responsive read latency will be
  580                  * in reaction to changes in write bandwidth. Unlike the classic
  581                  * boiler control PLL. this may result in over-steering while
  582                  * the SSD takes its time to react to the new, lower load. This
  583                  * is why we use a relatively low alpha of between .1 and .25 to
  584                  * compensate for this effect. At .1, it takes ~22 steering
  585                  * intervals to back off by a factor of 10. At .2 it only takes
  586                  * ~10. At .25 it only takes ~8. However some preliminary data
  587                  * from the SSD drives suggests a reasponse time in 10's of
  588                  * seconds before latency drops regardless of the new write
  589                  * rate. Careful observation will be reqiured to tune this
  590                  * effectively.
  591                  *
  592                  * Also, when there's no read traffic, we jack up the write
  593                  * limit too regardless of the last read latency.  10 is
  594                  * somewhat arbitrary.
  595                  */
  596                 if (lat < clp->lolat || isc->read_stats.total - clp->last_count < 10)
  597                         isc->write_stats.current = isc->write_stats.current *
  598                             (100 + clp->alpha) / 100;   /* Scale up */
  599                 else if (lat > clp->hilat)
  600                         isc->write_stats.current = isc->write_stats.current *
  601                             (100 - clp->alpha) / 100;   /* Scale down */
  602                 clp->last_count = isc->read_stats.total;
  603 
  604                 /*
  605                  * Even if we don't steer, per se, enforce the min/max limits as
  606                  * those may have changed.
  607                  */
  608                 if (isc->write_stats.current < isc->write_stats.min)
  609                         isc->write_stats.current = isc->write_stats.min;
  610                 if (isc->write_stats.current > isc->write_stats.max)
  611                         isc->write_stats.current = isc->write_stats.max;
  612                 if (old != isc->write_stats.current &&  iosched_debug)
  613                         printf("Steering write from %d kBps to %d kBps due to latency of %jdms\n",
  614                             old, isc->write_stats.current,
  615                             (uintmax_t)((uint64_t)1000000 * (uint32_t)lat) >> 32);
  616                 break;
  617         case cl_max:
  618                 break;
  619         }
  620 }
  621 #endif
  622 
  623                         /* Trim or similar currently pending completion */
  624 #define CAM_IOSCHED_FLAG_TRIM_ACTIVE    (1ul << 0)
  625                         /* Callout active, and needs to be torn down */
  626 #define CAM_IOSCHED_FLAG_CALLOUT_ACTIVE (1ul << 1)
  627 
  628                         /* Periph drivers set these flags to indicate work */
  629 #define CAM_IOSCHED_FLAG_WORK_FLAGS     ((0xffffu) << 16)
  630 
  631 #ifdef CAM_IOSCHED_DYNAMIC
  632 static void
  633 cam_iosched_io_metric_update(struct cam_iosched_softc *isc,
  634     sbintime_t sim_latency, int cmd, size_t size);
  635 #endif
  636 
  637 static inline int
  638 cam_iosched_has_flagged_work(struct cam_iosched_softc *isc)
  639 {
  640         return !!(isc->flags & CAM_IOSCHED_FLAG_WORK_FLAGS);
  641 }
  642 
  643 static inline int
  644 cam_iosched_has_io(struct cam_iosched_softc *isc)
  645 {
  646 #ifdef CAM_IOSCHED_DYNAMIC
  647         if (do_dynamic_iosched) {
  648                 struct bio *rbp = bioq_first(&isc->bio_queue);
  649                 struct bio *wbp = bioq_first(&isc->write_queue);
  650                 int can_write = wbp != NULL &&
  651                     cam_iosched_limiter_caniop(&isc->write_stats, wbp) == 0;
  652                 int can_read = rbp != NULL &&
  653                     cam_iosched_limiter_caniop(&isc->read_stats, rbp) == 0;
  654                 if (iosched_debug > 2) {
  655                         printf("can write %d: pending_writes %d max_writes %d\n", can_write, isc->write_stats.pending, isc->write_stats.max);
  656                         printf("can read %d: read_stats.pending %d max_reads %d\n", can_read, isc->read_stats.pending, isc->read_stats.max);
  657                         printf("Queued reads %d writes %d\n", isc->read_stats.queued, isc->write_stats.queued);
  658                 }
  659                 return can_read || can_write;
  660         }
  661 #endif
  662         return bioq_first(&isc->bio_queue) != NULL;
  663 }
  664 
  665 static inline int
  666 cam_iosched_has_more_trim(struct cam_iosched_softc *isc)
  667 {
  668         return !(isc->flags & CAM_IOSCHED_FLAG_TRIM_ACTIVE) &&
  669             bioq_first(&isc->trim_queue);
  670 }
  671 
  672 #define cam_iosched_sort_queue(isc)     ((isc)->sort_io_queue >= 0 ?    \
  673     (isc)->sort_io_queue : cam_sort_io_queues)
  674 
  675 
  676 static inline int
  677 cam_iosched_has_work(struct cam_iosched_softc *isc)
  678 {
  679 #ifdef CAM_IOSCHED_DYNAMIC
  680         if (iosched_debug > 2)
  681                 printf("has work: %d %d %d\n", cam_iosched_has_io(isc),
  682                     cam_iosched_has_more_trim(isc),
  683                     cam_iosched_has_flagged_work(isc));
  684 #endif
  685 
  686         return cam_iosched_has_io(isc) ||
  687                 cam_iosched_has_more_trim(isc) ||
  688                 cam_iosched_has_flagged_work(isc);
  689 }
  690 
  691 #ifdef CAM_IOSCHED_DYNAMIC
  692 static void
  693 cam_iosched_iop_stats_init(struct cam_iosched_softc *isc, struct iop_stats *ios)
  694 {
  695 
  696         ios->limiter = none;
  697         cam_iosched_limiter_init(ios);
  698         ios->in = 0;
  699         ios->max = 300000;
  700         ios->min = 1;
  701         ios->out = 0;
  702         ios->pending = 0;
  703         ios->queued = 0;
  704         ios->total = 0;
  705         ios->ema = 0;
  706         ios->emss = 0;
  707         ios->sd = 0;
  708         ios->softc = isc;
  709 }
  710 
  711 static int
  712 cam_iosched_limiter_sysctl(SYSCTL_HANDLER_ARGS)
  713 {
  714         char buf[16];
  715         struct iop_stats *ios;
  716         struct cam_iosched_softc *isc;
  717         int value, i, error, cantick;
  718         const char *p;
  719         
  720         ios = arg1;
  721         isc = ios->softc;
  722         value = ios->limiter;
  723         if (value < none || value >= limiter_max)
  724                 p = "UNKNOWN";
  725         else
  726                 p = cam_iosched_limiter_names[value];
  727         
  728         strlcpy(buf, p, sizeof(buf));
  729         error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
  730         if (error != 0 || req->newptr == NULL)
  731                 return error;
  732 
  733         cam_periph_lock(isc->periph);
  734 
  735         for (i = none; i < limiter_max; i++) {
  736                 if (strcmp(buf, cam_iosched_limiter_names[i]) != 0)
  737                         continue;
  738                 ios->limiter = i;
  739                 error = cam_iosched_limiter_init(ios);
  740                 if (error != 0) {
  741                         ios->limiter = value;
  742                         cam_periph_unlock(isc->periph);
  743                         return error;
  744                 }
  745                 cantick = !!limsw[isc->read_stats.limiter].l_tick +
  746                     !!limsw[isc->write_stats.limiter].l_tick +
  747                     !!limsw[isc->trim_stats.limiter].l_tick +
  748                     1;  /* Control loop requires it */
  749                 if (isc->flags & CAM_IOSCHED_FLAG_CALLOUT_ACTIVE) {
  750                         if (cantick == 0) {
  751                                 callout_stop(&isc->ticker);
  752                                 isc->flags &= ~CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
  753                         }
  754                 } else {
  755                         if (cantick != 0) {
  756                                 callout_reset(&isc->ticker, hz / isc->quanta - 1, cam_iosched_ticker, isc);
  757                                 isc->flags |= CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
  758                         }
  759                 }
  760 
  761                 cam_periph_unlock(isc->periph);
  762                 return 0;
  763         }
  764 
  765         cam_periph_unlock(isc->periph);
  766         return EINVAL;
  767 }
  768 
  769 static int
  770 cam_iosched_control_type_sysctl(SYSCTL_HANDLER_ARGS)
  771 {
  772         char buf[16];
  773         struct control_loop *clp;
  774         struct cam_iosched_softc *isc;
  775         int value, i, error;
  776         const char *p;
  777         
  778         clp = arg1;
  779         isc = clp->softc;
  780         value = clp->type;
  781         if (value < none || value >= cl_max)
  782                 p = "UNKNOWN";
  783         else
  784                 p = cam_iosched_control_type_names[value];
  785         
  786         strlcpy(buf, p, sizeof(buf));
  787         error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
  788         if (error != 0 || req->newptr == NULL)
  789                 return error;
  790 
  791         for (i = set_max; i < cl_max; i++) {
  792                 if (strcmp(buf, cam_iosched_control_type_names[i]) != 0)
  793                         continue;
  794                 cam_periph_lock(isc->periph);
  795                 clp->type = i;
  796                 cam_periph_unlock(isc->periph);
  797                 return 0;
  798         }
  799 
  800         return EINVAL;
  801 }
  802 
  803 static int
  804 cam_iosched_sbintime_sysctl(SYSCTL_HANDLER_ARGS)
  805 {
  806         char buf[16];
  807         sbintime_t value;
  808         int error;
  809         uint64_t us;
  810         
  811         value = *(sbintime_t *)arg1;
  812         us = (uint64_t)value / SBT_1US;
  813         snprintf(buf, sizeof(buf), "%ju", (intmax_t)us);
  814         error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
  815         if (error != 0 || req->newptr == NULL)
  816                 return error;
  817         us = strtoul(buf, NULL, 10);
  818         if (us == 0)
  819                 return EINVAL;
  820         *(sbintime_t *)arg1 = us * SBT_1US;
  821         return 0;
  822 }
  823 
  824 static void
  825 cam_iosched_iop_stats_sysctl_init(struct cam_iosched_softc *isc, struct iop_stats *ios, char *name)
  826 {
  827         struct sysctl_oid_list *n;
  828         struct sysctl_ctx_list *ctx;
  829 
  830         ios->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
  831             SYSCTL_CHILDREN(isc->sysctl_tree), OID_AUTO, name,
  832             CTLFLAG_RD, 0, name);
  833         n = SYSCTL_CHILDREN(ios->sysctl_tree);
  834         ctx = &ios->sysctl_ctx;
  835 
  836         SYSCTL_ADD_UQUAD(ctx, n,
  837             OID_AUTO, "ema", CTLFLAG_RD,
  838             &ios->ema,
  839             "Fast Exponentially Weighted Moving Average");
  840         SYSCTL_ADD_UQUAD(ctx, n,
  841             OID_AUTO, "emss", CTLFLAG_RD,
  842             &ios->emss,
  843             "Fast Exponentially Weighted Moving Sum of Squares (maybe wrong)");
  844         SYSCTL_ADD_UQUAD(ctx, n,
  845             OID_AUTO, "sd", CTLFLAG_RD,
  846             &ios->sd,
  847             "Estimated SD for fast ema (may be wrong)");
  848 
  849         SYSCTL_ADD_INT(ctx, n,
  850             OID_AUTO, "pending", CTLFLAG_RD,
  851             &ios->pending, 0,
  852             "Instantaneous # of pending transactions");
  853         SYSCTL_ADD_INT(ctx, n,
  854             OID_AUTO, "count", CTLFLAG_RD,
  855             &ios->total, 0,
  856             "# of transactions submitted to hardware");
  857         SYSCTL_ADD_INT(ctx, n,
  858             OID_AUTO, "queued", CTLFLAG_RD,
  859             &ios->queued, 0,
  860             "# of transactions in the queue");
  861         SYSCTL_ADD_INT(ctx, n,
  862             OID_AUTO, "in", CTLFLAG_RD,
  863             &ios->in, 0,
  864             "# of transactions queued to driver");
  865         SYSCTL_ADD_INT(ctx, n,
  866             OID_AUTO, "out", CTLFLAG_RD,
  867             &ios->out, 0,
  868             "# of transactions completed");
  869 
  870         SYSCTL_ADD_PROC(ctx, n,
  871             OID_AUTO, "limiter", CTLTYPE_STRING | CTLFLAG_RW,
  872             ios, 0, cam_iosched_limiter_sysctl, "A",
  873             "Current limiting type.");
  874         SYSCTL_ADD_INT(ctx, n,
  875             OID_AUTO, "min", CTLFLAG_RW,
  876             &ios->min, 0,
  877             "min resource");
  878         SYSCTL_ADD_INT(ctx, n,
  879             OID_AUTO, "max", CTLFLAG_RW,
  880             &ios->max, 0,
  881             "max resource");
  882         SYSCTL_ADD_INT(ctx, n,
  883             OID_AUTO, "current", CTLFLAG_RW,
  884             &ios->current, 0,
  885             "current resource");
  886 
  887 }
  888 
  889 static void
  890 cam_iosched_iop_stats_fini(struct iop_stats *ios)
  891 {
  892         if (ios->sysctl_tree)
  893                 if (sysctl_ctx_free(&ios->sysctl_ctx) != 0)
  894                         printf("can't remove iosched sysctl stats context\n");
  895 }
  896 
  897 static void
  898 cam_iosched_cl_sysctl_init(struct cam_iosched_softc *isc)
  899 {
  900         struct sysctl_oid_list *n;
  901         struct sysctl_ctx_list *ctx;
  902         struct control_loop *clp;
  903         
  904         clp = &isc->cl;
  905         clp->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
  906             SYSCTL_CHILDREN(isc->sysctl_tree), OID_AUTO, "control",
  907             CTLFLAG_RD, 0, "Control loop info");
  908         n = SYSCTL_CHILDREN(clp->sysctl_tree);
  909         ctx = &clp->sysctl_ctx;
  910 
  911         SYSCTL_ADD_PROC(ctx, n,
  912             OID_AUTO, "type", CTLTYPE_STRING | CTLFLAG_RW,
  913             clp, 0, cam_iosched_control_type_sysctl, "A",
  914             "Control loop algorithm");
  915         SYSCTL_ADD_PROC(ctx, n,
  916             OID_AUTO, "steer_interval", CTLTYPE_STRING | CTLFLAG_RW,
  917             &clp->steer_interval, 0, cam_iosched_sbintime_sysctl, "A",
  918             "How often to steer (in us)");
  919         SYSCTL_ADD_PROC(ctx, n,
  920             OID_AUTO, "lolat", CTLTYPE_STRING | CTLFLAG_RW,
  921             &clp->lolat, 0, cam_iosched_sbintime_sysctl, "A",
  922             "Low water mark for Latency (in us)");
  923         SYSCTL_ADD_PROC(ctx, n,
  924             OID_AUTO, "hilat", CTLTYPE_STRING | CTLFLAG_RW,
  925             &clp->hilat, 0, cam_iosched_sbintime_sysctl, "A",
  926             "Hi water mark for Latency (in us)");
  927         SYSCTL_ADD_INT(ctx, n,
  928             OID_AUTO, "alpha", CTLFLAG_RW,
  929             &clp->alpha, 0,
  930             "Alpha for PLL (x100) aka gain");
  931 }
  932 
  933 static void
  934 cam_iosched_cl_sysctl_fini(struct control_loop *clp)
  935 {
  936         if (clp->sysctl_tree)
  937                 if (sysctl_ctx_free(&clp->sysctl_ctx) != 0)
  938                         printf("can't remove iosched sysctl control loop context\n");
  939 }
  940 #endif
  941             
  942 /*
  943  * Allocate the iosched structure. This also insulates callers from knowing
  944  * sizeof struct cam_iosched_softc.
  945  */
  946 int
  947 cam_iosched_init(struct cam_iosched_softc **iscp, struct cam_periph *periph)
  948 {
  949 
  950         *iscp = malloc(sizeof(**iscp), M_CAMSCHED, M_NOWAIT | M_ZERO);
  951         if (*iscp == NULL)
  952                 return ENOMEM;
  953 #ifdef CAM_IOSCHED_DYNAMIC
  954         if (iosched_debug)
  955                 printf("CAM IOSCHEDULER Allocating entry at %p\n", *iscp);
  956 #endif
  957         (*iscp)->sort_io_queue = -1;
  958         bioq_init(&(*iscp)->bio_queue);
  959         bioq_init(&(*iscp)->trim_queue);
  960 #ifdef CAM_IOSCHED_DYNAMIC
  961         if (do_dynamic_iosched) {
  962                 bioq_init(&(*iscp)->write_queue);
  963                 (*iscp)->read_bias = 100;
  964                 (*iscp)->current_read_bias = 100;
  965                 (*iscp)->quanta = 200;
  966                 cam_iosched_iop_stats_init(*iscp, &(*iscp)->read_stats);
  967                 cam_iosched_iop_stats_init(*iscp, &(*iscp)->write_stats);
  968                 cam_iosched_iop_stats_init(*iscp, &(*iscp)->trim_stats);
  969                 (*iscp)->trim_stats.max = 1;    /* Trims are special: one at a time for now */
  970                 (*iscp)->last_time = sbinuptime();
  971                 callout_init_mtx(&(*iscp)->ticker, cam_periph_mtx(periph), 0);
  972                 (*iscp)->periph = periph;
  973                 cam_iosched_cl_init(&(*iscp)->cl, *iscp);
  974                 callout_reset(&(*iscp)->ticker, hz / (*iscp)->quanta - 1, cam_iosched_ticker, *iscp);
  975                 (*iscp)->flags |= CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
  976         }
  977 #endif
  978 
  979         return 0;
  980 }
  981 
  982 /*
  983  * Reclaim all used resources. This assumes that other folks have
  984  * drained the requests in the hardware. Maybe an unwise assumption.
  985  */
  986 void
  987 cam_iosched_fini(struct cam_iosched_softc *isc)
  988 {
  989         if (isc) {
  990                 cam_iosched_flush(isc, NULL, ENXIO);
  991 #ifdef CAM_IOSCHED_DYNAMIC
  992                 cam_iosched_iop_stats_fini(&isc->read_stats);
  993                 cam_iosched_iop_stats_fini(&isc->write_stats);
  994                 cam_iosched_iop_stats_fini(&isc->trim_stats);
  995                 cam_iosched_cl_sysctl_fini(&isc->cl);
  996                 if (isc->sysctl_tree)
  997                         if (sysctl_ctx_free(&isc->sysctl_ctx) != 0)
  998                                 printf("can't remove iosched sysctl stats context\n");
  999                 if (isc->flags & CAM_IOSCHED_FLAG_CALLOUT_ACTIVE) {
 1000                         callout_drain(&isc->ticker);
 1001                         isc->flags &= ~ CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
 1002                 }
 1003                         
 1004 #endif
 1005                 free(isc, M_CAMSCHED);
 1006         }
 1007 }
 1008 
 1009 /*
 1010  * After we're sure we're attaching a device, go ahead and add
 1011  * hooks for any sysctl we may wish to honor.
 1012  */
 1013 void cam_iosched_sysctl_init(struct cam_iosched_softc *isc,
 1014     struct sysctl_ctx_list *ctx, struct sysctl_oid *node)
 1015 {
 1016 #ifdef CAM_IOSCHED_DYNAMIC
 1017         struct sysctl_oid_list *n;
 1018 #endif
 1019 
 1020         SYSCTL_ADD_INT(ctx, SYSCTL_CHILDREN(node),
 1021                 OID_AUTO, "sort_io_queue", CTLFLAG_RW | CTLFLAG_MPSAFE,
 1022                 &isc->sort_io_queue, 0,
 1023                 "Sort IO queue to try and optimise disk access patterns");
 1024 
 1025 #ifdef CAM_IOSCHED_DYNAMIC
 1026         if (!do_dynamic_iosched)
 1027                 return;
 1028 
 1029         isc->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
 1030             SYSCTL_CHILDREN(node), OID_AUTO, "iosched",
 1031             CTLFLAG_RD, 0, "I/O scheduler statistics");
 1032         n = SYSCTL_CHILDREN(isc->sysctl_tree);
 1033         ctx = &isc->sysctl_ctx;
 1034 
 1035         cam_iosched_iop_stats_sysctl_init(isc, &isc->read_stats, "read");
 1036         cam_iosched_iop_stats_sysctl_init(isc, &isc->write_stats, "write");
 1037         cam_iosched_iop_stats_sysctl_init(isc, &isc->trim_stats, "trim");
 1038         cam_iosched_cl_sysctl_init(isc);
 1039 
 1040         SYSCTL_ADD_INT(ctx, n,
 1041             OID_AUTO, "read_bias", CTLFLAG_RW,
 1042             &isc->read_bias, 100,
 1043             "How biased towards read should we be independent of limits");
 1044 
 1045         SYSCTL_ADD_INT(ctx, n,
 1046             OID_AUTO, "quanta", CTLFLAG_RW,
 1047             &isc->quanta, 200,
 1048             "How many quanta per second do we slice the I/O up into");
 1049 
 1050         SYSCTL_ADD_INT(ctx, n,
 1051             OID_AUTO, "total_ticks", CTLFLAG_RD,
 1052             &isc->total_ticks, 0,
 1053             "Total number of ticks we've done");
 1054 #endif
 1055 }
 1056 
 1057 /*
 1058  * Flush outstanding I/O. Consumers of this library don't know all the
 1059  * queues we may keep, so this allows all I/O to be flushed in one
 1060  * convenient call.
 1061  */
 1062 void
 1063 cam_iosched_flush(struct cam_iosched_softc *isc, struct devstat *stp, int err)
 1064 {
 1065         bioq_flush(&isc->bio_queue, stp, err);
 1066         bioq_flush(&isc->trim_queue, stp, err);
 1067 #ifdef CAM_IOSCHED_DYNAMIC
 1068         if (do_dynamic_iosched)
 1069                 bioq_flush(&isc->write_queue, stp, err);
 1070 #endif
 1071 }
 1072 
 1073 #ifdef CAM_IOSCHED_DYNAMIC
 1074 static struct bio *
 1075 cam_iosched_get_write(struct cam_iosched_softc *isc)
 1076 {
 1077         struct bio *bp;
 1078 
 1079         /*
 1080          * We control the write rate by controlling how many requests we send
 1081          * down to the drive at any one time. Fewer requests limits the
 1082          * effects of both starvation when the requests take a while and write
 1083          * amplification when each request is causing more than one write to
 1084          * the NAND media. Limiting the queue depth like this will also limit
 1085          * the write throughput and give and reads that want to compete to
 1086          * compete unfairly.
 1087          */
 1088         bp = bioq_first(&isc->write_queue);
 1089         if (bp == NULL) {
 1090                 if (iosched_debug > 3)
 1091                         printf("No writes present in write_queue\n");
 1092                 return NULL;
 1093         }
 1094 
 1095         /*
 1096          * If pending read, prefer that based on current read bias
 1097          * setting.
 1098          */
 1099         if (bioq_first(&isc->bio_queue) && isc->current_read_bias) {
 1100                 if (iosched_debug)
 1101                         printf("Reads present and current_read_bias is %d queued writes %d queued reads %d\n", isc->current_read_bias, isc->write_stats.queued, isc->read_stats.queued);
 1102                 isc->current_read_bias--;
 1103                 return NULL;
 1104         }
 1105 
 1106         /*
 1107          * See if our current limiter allows this I/O.
 1108          */
 1109         if (cam_iosched_limiter_iop(&isc->write_stats, bp) != 0) {
 1110                 if (iosched_debug)
 1111                         printf("Can't write because limiter says no.\n");
 1112                 return NULL;
 1113         }
 1114 
 1115         /*
 1116          * Let's do this: We've passed all the gates and we're a go
 1117          * to schedule the I/O in the SIM.
 1118          */
 1119         isc->current_read_bias = isc->read_bias;
 1120         bioq_remove(&isc->write_queue, bp);
 1121         if (bp->bio_cmd == BIO_WRITE) {
 1122                 isc->write_stats.queued--;
 1123                 isc->write_stats.total++;
 1124                 isc->write_stats.pending++;
 1125         }
 1126         if (iosched_debug > 9)
 1127                 printf("HWQ : %p %#x\n", bp, bp->bio_cmd);
 1128         return bp;
 1129 }
 1130 #endif
 1131 
 1132 /*
 1133  * Put back a trim that you weren't able to actually schedule this time.
 1134  */
 1135 void
 1136 cam_iosched_put_back_trim(struct cam_iosched_softc *isc, struct bio *bp)
 1137 {
 1138         bioq_insert_head(&isc->trim_queue, bp);
 1139 #ifdef CAM_IOSCHED_DYNAMIC
 1140         isc->trim_stats.queued++;
 1141         isc->trim_stats.total--;                /* since we put it back, don't double count */
 1142         isc->trim_stats.pending--;
 1143 #endif
 1144 }
 1145 
 1146 /*
 1147  * gets the next trim from the trim queue.
 1148  *
 1149  * Assumes we're called with the periph lock held.  It removes this
 1150  * trim from the queue and the device must explicitly reinstert it
 1151  * should the need arise.
 1152  */
 1153 struct bio *
 1154 cam_iosched_next_trim(struct cam_iosched_softc *isc)
 1155 {
 1156         struct bio *bp;
 1157 
 1158         bp  = bioq_first(&isc->trim_queue);
 1159         if (bp == NULL)
 1160                 return NULL;
 1161         bioq_remove(&isc->trim_queue, bp);
 1162 #ifdef CAM_IOSCHED_DYNAMIC
 1163         isc->trim_stats.queued--;
 1164         isc->trim_stats.total++;
 1165         isc->trim_stats.pending++;
 1166 #endif
 1167         return bp;
 1168 }
 1169 
 1170 /*
 1171  * gets the an available trim from the trim queue, if there's no trim
 1172  * already pending. It removes this trim from the queue and the device
 1173  * must explicitly reinstert it should the need arise.
 1174  *
 1175  * Assumes we're called with the periph lock held.
 1176  */
 1177 struct bio *
 1178 cam_iosched_get_trim(struct cam_iosched_softc *isc)
 1179 {
 1180 
 1181         if (!cam_iosched_has_more_trim(isc))
 1182                 return NULL;
 1183 
 1184         return cam_iosched_next_trim(isc);
 1185 }
 1186 
 1187 /*
 1188  * Determine what the next bit of work to do is for the periph. The
 1189  * default implementation looks to see if we have trims to do, but no
 1190  * trims outstanding. If so, we do that. Otherwise we see if we have
 1191  * other work. If we do, then we do that. Otherwise why were we called?
 1192  */
 1193 struct bio *
 1194 cam_iosched_next_bio(struct cam_iosched_softc *isc)
 1195 {
 1196         struct bio *bp;
 1197 
 1198         /*
 1199          * See if we have a trim that can be scheduled. We can only send one
 1200          * at a time down, so this takes that into account.
 1201          *
 1202          * XXX newer TRIM commands are queueable. Revisit this when we
 1203          * implement them.
 1204          */
 1205         if ((bp = cam_iosched_get_trim(isc)) != NULL)
 1206                 return bp;
 1207 
 1208 #ifdef CAM_IOSCHED_DYNAMIC
 1209         /*
 1210          * See if we have any pending writes, and room in the queue for them,
 1211          * and if so, those are next.
 1212          */
 1213         if (do_dynamic_iosched) {
 1214                 if ((bp = cam_iosched_get_write(isc)) != NULL)
 1215                         return bp;
 1216         }
 1217 #endif
 1218 
 1219         /*
 1220          * next, see if there's other, normal I/O waiting. If so return that.
 1221          */
 1222         if ((bp = bioq_first(&isc->bio_queue)) == NULL)
 1223                 return NULL;
 1224 
 1225 #ifdef CAM_IOSCHED_DYNAMIC
 1226         /*
 1227          * For the netflix scheduler, bio_queue is only for reads, so enforce
 1228          * the limits here. Enforce only for reads.
 1229          */
 1230         if (do_dynamic_iosched) {
 1231                 if (bp->bio_cmd == BIO_READ &&
 1232                     cam_iosched_limiter_iop(&isc->read_stats, bp) != 0)
 1233                         return NULL;
 1234         }
 1235 #endif
 1236         bioq_remove(&isc->bio_queue, bp);
 1237 #ifdef CAM_IOSCHED_DYNAMIC
 1238         if (do_dynamic_iosched) {
 1239                 if (bp->bio_cmd == BIO_READ) {
 1240                         isc->read_stats.queued--;
 1241                         isc->read_stats.total++;
 1242                         isc->read_stats.pending++;
 1243                 } else
 1244                         printf("Found bio_cmd = %#x\n", bp->bio_cmd);
 1245         }
 1246         if (iosched_debug > 9)
 1247                 printf("HWQ : %p %#x\n", bp, bp->bio_cmd);
 1248 #endif
 1249         return bp;
 1250 }
 1251         
 1252 /*
 1253  * Driver has been given some work to do by the block layer. Tell the
 1254  * scheduler about it and have it queue the work up. The scheduler module
 1255  * will then return the currently most useful bit of work later, possibly
 1256  * deferring work for various reasons.
 1257  */
 1258 void
 1259 cam_iosched_queue_work(struct cam_iosched_softc *isc, struct bio *bp)
 1260 {
 1261 
 1262         /*
 1263          * Put all trims on the trim queue sorted, since we know
 1264          * that the collapsing code requires this. Otherwise put
 1265          * the work on the bio queue.
 1266          */
 1267         if (bp->bio_cmd == BIO_DELETE) {
 1268                 bioq_disksort(&isc->trim_queue, bp);
 1269 #ifdef CAM_IOSCHED_DYNAMIC
 1270                 isc->trim_stats.in++;
 1271                 isc->trim_stats.queued++;
 1272 #endif
 1273         }
 1274 #ifdef CAM_IOSCHED_DYNAMIC
 1275         else if (do_dynamic_iosched &&
 1276             (bp->bio_cmd == BIO_WRITE || bp->bio_cmd == BIO_FLUSH)) {
 1277                 if (cam_iosched_sort_queue(isc))
 1278                         bioq_disksort(&isc->write_queue, bp);
 1279                 else
 1280                         bioq_insert_tail(&isc->write_queue, bp);
 1281                 if (iosched_debug > 9)
 1282                         printf("Qw  : %p %#x\n", bp, bp->bio_cmd);
 1283                 if (bp->bio_cmd == BIO_WRITE) {
 1284                         isc->write_stats.in++;
 1285                         isc->write_stats.queued++;
 1286                 }
 1287         }
 1288 #endif
 1289         else {
 1290                 if (cam_iosched_sort_queue(isc))
 1291                         bioq_disksort(&isc->bio_queue, bp);
 1292                 else
 1293                         bioq_insert_tail(&isc->bio_queue, bp);
 1294 #ifdef CAM_IOSCHED_DYNAMIC
 1295                 if (iosched_debug > 9)
 1296                         printf("Qr  : %p %#x\n", bp, bp->bio_cmd);
 1297                 if (bp->bio_cmd == BIO_READ) {
 1298                         isc->read_stats.in++;
 1299                         isc->read_stats.queued++;
 1300                 } else if (bp->bio_cmd == BIO_WRITE) {
 1301                         isc->write_stats.in++;
 1302                         isc->write_stats.queued++;
 1303                 }
 1304 #endif
 1305         }
 1306 }
 1307 
 1308 /* 
 1309  * If we have work, get it scheduled. Called with the periph lock held.
 1310  */
 1311 void
 1312 cam_iosched_schedule(struct cam_iosched_softc *isc, struct cam_periph *periph)
 1313 {
 1314 
 1315         if (cam_iosched_has_work(isc))
 1316                 xpt_schedule(periph, CAM_PRIORITY_NORMAL);
 1317 }
 1318 
 1319 /*
 1320  * Complete a trim request
 1321  */
 1322 void
 1323 cam_iosched_trim_done(struct cam_iosched_softc *isc)
 1324 {
 1325 
 1326         isc->flags &= ~CAM_IOSCHED_FLAG_TRIM_ACTIVE;
 1327 }
 1328 
 1329 /*
 1330  * Complete a bio. Called before we release the ccb with xpt_release_ccb so we
 1331  * might use notes in the ccb for statistics.
 1332  */
 1333 int
 1334 cam_iosched_bio_complete(struct cam_iosched_softc *isc, struct bio *bp,
 1335     union ccb *done_ccb)
 1336 {
 1337         int retval = 0;
 1338 #ifdef CAM_IOSCHED_DYNAMIC
 1339         if (!do_dynamic_iosched)
 1340                 return retval;
 1341 
 1342         if (iosched_debug > 10)
 1343                 printf("done: %p %#x\n", bp, bp->bio_cmd);
 1344         if (bp->bio_cmd == BIO_WRITE) {
 1345                 retval = cam_iosched_limiter_iodone(&isc->write_stats, bp);
 1346                 isc->write_stats.out++;
 1347                 isc->write_stats.pending--;
 1348         } else if (bp->bio_cmd == BIO_READ) {
 1349                 retval = cam_iosched_limiter_iodone(&isc->read_stats, bp);
 1350                 isc->read_stats.out++;
 1351                 isc->read_stats.pending--;
 1352         } else if (bp->bio_cmd == BIO_DELETE) {
 1353                 isc->trim_stats.out++;
 1354                 isc->trim_stats.pending--;
 1355         } else if (bp->bio_cmd != BIO_FLUSH) {
 1356                 if (iosched_debug)
 1357                         printf("Completing command with bio_cmd == %#x\n", bp->bio_cmd);
 1358         }
 1359 
 1360         if (!(bp->bio_flags & BIO_ERROR))
 1361                 cam_iosched_io_metric_update(isc, done_ccb->ccb_h.qos.sim_data,
 1362                     bp->bio_cmd, bp->bio_bcount);
 1363 #endif
 1364         return retval;
 1365 }
 1366 
 1367 /*
 1368  * Tell the io scheduler that you've pushed a trim down into the sim.
 1369  * xxx better place for this?
 1370  */
 1371 void
 1372 cam_iosched_submit_trim(struct cam_iosched_softc *isc)
 1373 {
 1374 
 1375         isc->flags |= CAM_IOSCHED_FLAG_TRIM_ACTIVE;
 1376 }
 1377 
 1378 /*
 1379  * Change the sorting policy hint for I/O transactions for this device.
 1380  */
 1381 void
 1382 cam_iosched_set_sort_queue(struct cam_iosched_softc *isc, int val)
 1383 {
 1384 
 1385         isc->sort_io_queue = val;
 1386 }
 1387 
 1388 int
 1389 cam_iosched_has_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
 1390 {
 1391         return isc->flags & flags;
 1392 }
 1393 
 1394 void
 1395 cam_iosched_set_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
 1396 {
 1397         isc->flags |= flags;
 1398 }
 1399 
 1400 void
 1401 cam_iosched_clr_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
 1402 {
 1403         isc->flags &= ~flags;
 1404 }
 1405 
 1406 #ifdef CAM_IOSCHED_DYNAMIC
 1407 /*
 1408  * After the method presented in Jack Crenshaw's 1998 article "Integer
 1409  * Suqare Roots," reprinted at
 1410  * http://www.embedded.com/electronics-blogs/programmer-s-toolbox/4219659/Integer-Square-Roots
 1411  * and well worth the read. Briefly, we find the power of 4 that's the
 1412  * largest smaller than val. We then check each smaller power of 4 to
 1413  * see if val is still bigger. The right shifts at each step divide
 1414  * the result by 2 which after successive application winds up
 1415  * accumulating the right answer. It could also have been accumulated
 1416  * using a separate root counter, but this code is smaller and faster
 1417  * than that method. This method is also integer size invariant.
 1418  * It returns floor(sqrt((float)val)), or the larget integer less than
 1419  * or equal to the square root.
 1420  */
 1421 static uint64_t
 1422 isqrt64(uint64_t val)
 1423 {
 1424         uint64_t res = 0;
 1425         uint64_t bit = 1ULL << (sizeof(uint64_t) * NBBY - 2);
 1426 
 1427         /*
 1428          * Find the largest power of 4 smaller than val.
 1429          */
 1430         while (bit > val)
 1431                 bit >>= 2;
 1432 
 1433         /*
 1434          * Accumulate the answer, one bit at a time (we keep moving
 1435          * them over since 2 is the square root of 4 and we test
 1436          * powers of 4). We accumulate where we find the bit, but
 1437          * the successive shifts land the bit in the right place
 1438          * by the end.
 1439          */
 1440         while (bit != 0) {
 1441                 if (val >= res + bit) {
 1442                         val -= res + bit;
 1443                         res = (res >> 1) + bit;
 1444                 } else
 1445                         res >>= 1;
 1446                 bit >>= 2;
 1447         }
 1448         
 1449         return res;
 1450 }
 1451 
 1452 /*
 1453  * a and b are 32.32 fixed point stored in a 64-bit word.
 1454  * Let al and bl be the .32 part of a and b.
 1455  * Let ah and bh be the 32 part of a and b.
 1456  * R is the radix and is 1 << 32
 1457  *
 1458  * a * b
 1459  * (ah + al / R) * (bh + bl / R)
 1460  * ah * bh + (al * bh + ah * bl) / R + al * bl / R^2
 1461  *
 1462  * After multiplicaiton, we have to renormalize by multiply by
 1463  * R, so we wind up with
 1464  *      ah * bh * R + al * bh + ah * bl + al * bl / R
 1465  * which turns out to be a very nice way to compute this value
 1466  * so long as ah and bh are < 65536 there's no loss of high bits
 1467  * and the low order bits are below the threshold of caring for
 1468  * this application.
 1469  */
 1470 static uint64_t
 1471 mul(uint64_t a, uint64_t b)
 1472 {
 1473         uint64_t al, ah, bl, bh;
 1474         al = a & 0xffffffff;
 1475         ah = a >> 32;
 1476         bl = b & 0xffffffff;
 1477         bh = b >> 32;
 1478         return ((ah * bh) << 32) + al * bh + ah * bl + ((al * bl) >> 32);
 1479 }
 1480 
 1481 static void
 1482 cam_iosched_update(struct iop_stats *iop, sbintime_t sim_latency)
 1483 {
 1484         sbintime_t y, yy;
 1485         uint64_t var;
 1486 
 1487         /* 
 1488          * Classic expoentially decaying average with a tiny alpha
 1489          * (2 ^ -alpha_bits). For more info see the NIST statistical
 1490          * handbook.
 1491          *
 1492          * ema_t = y_t * alpha + ema_t-1 * (1 - alpha)
 1493          * alpha = 1 / (1 << alpha_bits)
 1494          *
 1495          * Since alpha is a power of two, we can compute this w/o any mult or
 1496          * division.
 1497          */
 1498         y = sim_latency;
 1499         iop->ema = (y + (iop->ema << alpha_bits) - iop->ema) >> alpha_bits;
 1500 
 1501         yy = mul(y, y);
 1502         iop->emss = (yy + (iop->emss << alpha_bits) - iop->emss) >> alpha_bits;
 1503 
 1504         /*
 1505          * s_1 = sum of data
 1506          * s_2 = sum of data * data
 1507          * ema ~ mean (or s_1 / N)
 1508          * emss ~ s_2 / N
 1509          *
 1510          * sd = sqrt((N * s_2 - s_1 ^ 2) / (N * (N - 1)))
 1511          * sd = sqrt((N * s_2 / N * (N - 1)) - (s_1 ^ 2 / (N * (N - 1))))
 1512          *
 1513          * N ~ 2 / alpha - 1
 1514          * alpha < 1 / 16 (typically much less)
 1515          * N > 31 --> N large so N * (N - 1) is approx N * N
 1516          *
 1517          * substituting and rearranging:
 1518          * sd ~ sqrt(s_2 / N - (s_1 / N) ^ 2)
 1519          *    ~ sqrt(emss - ema ^ 2);
 1520          * which is the formula used here to get a decent estimate of sd which
 1521          * we use to detect outliers. Note that when first starting up, it
 1522          * takes a while for emss sum of squares estimator to converge on a
 1523          * good value.  during this time, it can be less than ema^2. We
 1524          * compute a sd of 0 in that case, and ignore outliers.
 1525          */
 1526         var = iop->emss - mul(iop->ema, iop->ema);
 1527         iop->sd = (int64_t)var < 0 ? 0 : isqrt64(var);
 1528 }
 1529 
 1530 #ifdef CAM_IOSCHED_DYNAMIC
 1531 static void
 1532 cam_iosched_io_metric_update(struct cam_iosched_softc *isc,
 1533     sbintime_t sim_latency, int cmd, size_t size)
 1534 {
 1535         /* xxx Do we need to scale based on the size of the I/O ? */
 1536         switch (cmd) {
 1537         case BIO_READ:
 1538                 cam_iosched_update(&isc->read_stats, sim_latency);
 1539                 break;
 1540         case BIO_WRITE:
 1541                 cam_iosched_update(&isc->write_stats, sim_latency);
 1542                 break;
 1543         case BIO_DELETE:
 1544                 cam_iosched_update(&isc->trim_stats, sim_latency);
 1545                 break;
 1546         default:
 1547                 break;
 1548         }
 1549 }
 1550 #endif
 1551 
 1552 #ifdef DDB
 1553 static int biolen(struct bio_queue_head *bq)
 1554 {
 1555         int i = 0;
 1556         struct bio *bp;
 1557 
 1558         TAILQ_FOREACH(bp, &bq->queue, bio_queue) {
 1559                 i++;
 1560         }
 1561         return i;
 1562 }
 1563 
 1564 /*
 1565  * Show the internal state of the I/O scheduler.
 1566  */
 1567 DB_SHOW_COMMAND(iosched, cam_iosched_db_show)
 1568 {
 1569         struct cam_iosched_softc *isc;
 1570 
 1571         if (!have_addr) {
 1572                 db_printf("Need addr\n");
 1573                 return;
 1574         }
 1575         isc = (struct cam_iosched_softc *)addr;
 1576         db_printf("pending_reads:     %d\n", isc->read_stats.pending);
 1577         db_printf("min_reads:         %d\n", isc->read_stats.min);
 1578         db_printf("max_reads:         %d\n", isc->read_stats.max);
 1579         db_printf("reads:             %d\n", isc->read_stats.total);
 1580         db_printf("in_reads:          %d\n", isc->read_stats.in);
 1581         db_printf("out_reads:         %d\n", isc->read_stats.out);
 1582         db_printf("queued_reads:      %d\n", isc->read_stats.queued);
 1583         db_printf("Current Q len      %d\n", biolen(&isc->bio_queue));
 1584         db_printf("pending_writes:    %d\n", isc->write_stats.pending);
 1585         db_printf("min_writes:        %d\n", isc->write_stats.min);
 1586         db_printf("max_writes:        %d\n", isc->write_stats.max);
 1587         db_printf("writes:            %d\n", isc->write_stats.total);
 1588         db_printf("in_writes:         %d\n", isc->write_stats.in);
 1589         db_printf("out_writes:        %d\n", isc->write_stats.out);
 1590         db_printf("queued_writes:     %d\n", isc->write_stats.queued);
 1591         db_printf("Current Q len      %d\n", biolen(&isc->write_queue));
 1592         db_printf("pending_trims:     %d\n", isc->trim_stats.pending);
 1593         db_printf("min_trims:         %d\n", isc->trim_stats.min);
 1594         db_printf("max_trims:         %d\n", isc->trim_stats.max);
 1595         db_printf("trims:             %d\n", isc->trim_stats.total);
 1596         db_printf("in_trims:          %d\n", isc->trim_stats.in);
 1597         db_printf("out_trims:         %d\n", isc->trim_stats.out);
 1598         db_printf("queued_trims:      %d\n", isc->trim_stats.queued);
 1599         db_printf("Current Q len      %d\n", biolen(&isc->trim_queue));
 1600         db_printf("read_bias:         %d\n", isc->read_bias);
 1601         db_printf("current_read_bias: %d\n", isc->current_read_bias);
 1602         db_printf("Trim active?       %s\n", 
 1603             (isc->flags & CAM_IOSCHED_FLAG_TRIM_ACTIVE) ? "yes" : "no");
 1604 }
 1605 #endif
 1606 #endif

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