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

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    1 /*-
    2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
    3  *
    4  * Copyright (c) 2001-2002 Luigi Rizzo
    5  *
    6  * Supported by: the Xorp Project (www.xorp.org)
    7  *
    8  * Redistribution and use in source and binary forms, with or without
    9  * modification, are permitted provided that the following conditions
   10  * are met:
   11  * 1. Redistributions of source code must retain the above copyright
   12  *    notice, this list of conditions and the following disclaimer.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice, this list of conditions and the following disclaimer in the
   15  *    documentation and/or other materials provided with the distribution.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
   21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   27  * SUCH DAMAGE.
   28  */
   29 
   30 #include <sys/cdefs.h>
   31 __FBSDID("$FreeBSD$");
   32 
   33 #include "opt_device_polling.h"
   34 
   35 #include <sys/param.h>
   36 #include <sys/systm.h>
   37 #include <sys/kernel.h>
   38 #include <sys/kthread.h>
   39 #include <sys/proc.h>
   40 #include <sys/epoch.h>
   41 #include <sys/eventhandler.h>
   42 #include <sys/resourcevar.h>
   43 #include <sys/socket.h>                 /* needed by net/if.h           */
   44 #include <sys/sockio.h>
   45 #include <sys/sysctl.h>
   46 #include <sys/syslog.h>
   47 
   48 #include <net/if.h>
   49 #include <net/if_var.h>
   50 #include <net/netisr.h>                 /* for NETISR_POLL              */
   51 #include <net/vnet.h>
   52 
   53 void hardclock_device_poll(void);       /* hook from hardclock          */
   54 
   55 static struct mtx       poll_mtx;
   56 
   57 /*
   58  * Polling support for [network] device drivers.
   59  *
   60  * Drivers which support this feature can register with the
   61  * polling code.
   62  *
   63  * If registration is successful, the driver must disable interrupts,
   64  * and further I/O is performed through the handler, which is invoked
   65  * (at least once per clock tick) with 3 arguments: the "arg" passed at
   66  * register time (a struct ifnet pointer), a command, and a "count" limit.
   67  *
   68  * The command can be one of the following:
   69  *  POLL_ONLY: quick move of "count" packets from input/output queues.
   70  *  POLL_AND_CHECK_STATUS: as above, plus check status registers or do
   71  *      other more expensive operations. This command is issued periodically
   72  *      but less frequently than POLL_ONLY.
   73  *
   74  * The count limit specifies how much work the handler can do during the
   75  * call -- typically this is the number of packets to be received, or
   76  * transmitted, etc. (drivers are free to interpret this number, as long
   77  * as the max time spent in the function grows roughly linearly with the
   78  * count).
   79  *
   80  * Polling is enabled and disabled via setting IFCAP_POLLING flag on
   81  * the interface. The driver ioctl handler should register interface
   82  * with polling and disable interrupts, if registration was successful.
   83  *
   84  * A second variable controls the sharing of CPU between polling/kernel
   85  * network processing, and other activities (typically userlevel tasks):
   86  * kern.polling.user_frac (between 0 and 100, default 50) sets the share
   87  * of CPU allocated to user tasks. CPU is allocated proportionally to the
   88  * shares, by dynamically adjusting the "count" (poll_burst).
   89  *
   90  * Other parameters can should be left to their default values.
   91  * The following constraints hold
   92  *
   93  *      1 <= poll_each_burst <= poll_burst <= poll_burst_max
   94  *      MIN_POLL_BURST_MAX <= poll_burst_max <= MAX_POLL_BURST_MAX
   95  */
   96 
   97 #define MIN_POLL_BURST_MAX      10
   98 #define MAX_POLL_BURST_MAX      20000
   99 
  100 static uint32_t poll_burst = 5;
  101 static uint32_t poll_burst_max = 150;   /* good for 100Mbit net and HZ=1000 */
  102 static uint32_t poll_each_burst = 5;
  103 
  104 static SYSCTL_NODE(_kern, OID_AUTO, polling, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
  105     "Device polling parameters");
  106 
  107 SYSCTL_UINT(_kern_polling, OID_AUTO, burst, CTLFLAG_RD,
  108         &poll_burst, 0, "Current polling burst size");
  109 
  110 static int      netisr_poll_scheduled;
  111 static int      netisr_pollmore_scheduled;
  112 static int      poll_shutting_down;
  113 
  114 static int poll_burst_max_sysctl(SYSCTL_HANDLER_ARGS)
  115 {
  116         uint32_t val = poll_burst_max;
  117         int error;
  118 
  119         error = sysctl_handle_int(oidp, &val, 0, req);
  120         if (error || !req->newptr )
  121                 return (error);
  122         if (val < MIN_POLL_BURST_MAX || val > MAX_POLL_BURST_MAX)
  123                 return (EINVAL);
  124 
  125         mtx_lock(&poll_mtx);
  126         poll_burst_max = val;
  127         if (poll_burst > poll_burst_max)
  128                 poll_burst = poll_burst_max;
  129         if (poll_each_burst > poll_burst_max)
  130                 poll_each_burst = MIN_POLL_BURST_MAX;
  131         mtx_unlock(&poll_mtx);
  132 
  133         return (0);
  134 }
  135 SYSCTL_PROC(_kern_polling, OID_AUTO, burst_max,
  136     CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_MPSAFE, 0, sizeof(uint32_t),
  137     poll_burst_max_sysctl, "I",
  138     "Max Polling burst size");
  139 
  140 static int poll_each_burst_sysctl(SYSCTL_HANDLER_ARGS)
  141 {
  142         uint32_t val = poll_each_burst;
  143         int error;
  144 
  145         error = sysctl_handle_int(oidp, &val, 0, req);
  146         if (error || !req->newptr )
  147                 return (error);
  148         if (val < 1)
  149                 return (EINVAL);
  150 
  151         mtx_lock(&poll_mtx);
  152         if (val > poll_burst_max) {
  153                 mtx_unlock(&poll_mtx);
  154                 return (EINVAL);
  155         }
  156         poll_each_burst = val;
  157         mtx_unlock(&poll_mtx);
  158 
  159         return (0);
  160 }
  161 SYSCTL_PROC(_kern_polling, OID_AUTO, each_burst,
  162     CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_MPSAFE, 0, sizeof(uint32_t),
  163     poll_each_burst_sysctl, "I",
  164     "Max size of each burst");
  165 
  166 static uint32_t poll_in_idle_loop=0;    /* do we poll in idle loop ? */
  167 SYSCTL_UINT(_kern_polling, OID_AUTO, idle_poll, CTLFLAG_RW,
  168         &poll_in_idle_loop, 0, "Enable device polling in idle loop");
  169 
  170 static uint32_t user_frac = 50;
  171 static int user_frac_sysctl(SYSCTL_HANDLER_ARGS)
  172 {
  173         uint32_t val = user_frac;
  174         int error;
  175 
  176         error = sysctl_handle_int(oidp, &val, 0, req);
  177         if (error || !req->newptr )
  178                 return (error);
  179         if (val > 99)
  180                 return (EINVAL);
  181 
  182         mtx_lock(&poll_mtx);
  183         user_frac = val;
  184         mtx_unlock(&poll_mtx);
  185 
  186         return (0);
  187 }
  188 SYSCTL_PROC(_kern_polling, OID_AUTO, user_frac,
  189     CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_MPSAFE, 0, sizeof(uint32_t),
  190     user_frac_sysctl, "I",
  191     "Desired user fraction of cpu time");
  192 
  193 static uint32_t reg_frac_count = 0;
  194 static uint32_t reg_frac = 20 ;
  195 static int reg_frac_sysctl(SYSCTL_HANDLER_ARGS)
  196 {
  197         uint32_t val = reg_frac;
  198         int error;
  199 
  200         error = sysctl_handle_int(oidp, &val, 0, req);
  201         if (error || !req->newptr )
  202                 return (error);
  203         if (val < 1 || val > hz)
  204                 return (EINVAL);
  205 
  206         mtx_lock(&poll_mtx);
  207         reg_frac = val;
  208         if (reg_frac_count >= reg_frac)
  209                 reg_frac_count = 0;
  210         mtx_unlock(&poll_mtx);
  211 
  212         return (0);
  213 }
  214 SYSCTL_PROC(_kern_polling, OID_AUTO, reg_frac,
  215     CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_MPSAFE, 0, sizeof(uint32_t),
  216     reg_frac_sysctl, "I",
  217     "Every this many cycles check registers");
  218 
  219 static uint32_t short_ticks;
  220 SYSCTL_UINT(_kern_polling, OID_AUTO, short_ticks, CTLFLAG_RD,
  221         &short_ticks, 0, "Hardclock ticks shorter than they should be");
  222 
  223 static uint32_t lost_polls;
  224 SYSCTL_UINT(_kern_polling, OID_AUTO, lost_polls, CTLFLAG_RD,
  225         &lost_polls, 0, "How many times we would have lost a poll tick");
  226 
  227 static uint32_t pending_polls;
  228 SYSCTL_UINT(_kern_polling, OID_AUTO, pending_polls, CTLFLAG_RD,
  229         &pending_polls, 0, "Do we need to poll again");
  230 
  231 static int residual_burst = 0;
  232 SYSCTL_INT(_kern_polling, OID_AUTO, residual_burst, CTLFLAG_RD,
  233         &residual_burst, 0, "# of residual cycles in burst");
  234 
  235 static uint32_t poll_handlers; /* next free entry in pr[]. */
  236 SYSCTL_UINT(_kern_polling, OID_AUTO, handlers, CTLFLAG_RD,
  237         &poll_handlers, 0, "Number of registered poll handlers");
  238 
  239 static uint32_t phase;
  240 SYSCTL_UINT(_kern_polling, OID_AUTO, phase, CTLFLAG_RD,
  241         &phase, 0, "Polling phase");
  242 
  243 static uint32_t suspect;
  244 SYSCTL_UINT(_kern_polling, OID_AUTO, suspect, CTLFLAG_RD,
  245         &suspect, 0, "suspect event");
  246 
  247 static uint32_t stalled;
  248 SYSCTL_UINT(_kern_polling, OID_AUTO, stalled, CTLFLAG_RD,
  249         &stalled, 0, "potential stalls");
  250 
  251 static uint32_t idlepoll_sleeping; /* idlepoll is sleeping */
  252 SYSCTL_UINT(_kern_polling, OID_AUTO, idlepoll_sleeping, CTLFLAG_RD,
  253         &idlepoll_sleeping, 0, "idlepoll is sleeping");
  254 
  255 #define POLL_LIST_LEN  128
  256 struct pollrec {
  257         poll_handler_t  *handler;
  258         struct ifnet    *ifp;
  259 };
  260 
  261 static struct pollrec pr[POLL_LIST_LEN];
  262 
  263 static void
  264 poll_shutdown(void *arg, int howto)
  265 {
  266 
  267         poll_shutting_down = 1;
  268 }
  269 
  270 static void
  271 init_device_poll(void)
  272 {
  273 
  274         mtx_init(&poll_mtx, "polling", NULL, MTX_DEF);
  275         EVENTHANDLER_REGISTER(shutdown_post_sync, poll_shutdown, NULL,
  276             SHUTDOWN_PRI_LAST);
  277 }
  278 SYSINIT(device_poll, SI_SUB_SOFTINTR, SI_ORDER_MIDDLE, init_device_poll, NULL);
  279 
  280 /*
  281  * Hook from hardclock. Tries to schedule a netisr, but keeps track
  282  * of lost ticks due to the previous handler taking too long.
  283  * Normally, this should not happen, because polling handler should
  284  * run for a short time. However, in some cases (e.g. when there are
  285  * changes in link status etc.) the drivers take a very long time
  286  * (even in the order of milliseconds) to reset and reconfigure the
  287  * device, causing apparent lost polls.
  288  *
  289  * The first part of the code is just for debugging purposes, and tries
  290  * to count how often hardclock ticks are shorter than they should,
  291  * meaning either stray interrupts or delayed events.
  292  */
  293 void
  294 hardclock_device_poll(void)
  295 {
  296         static struct timeval prev_t, t;
  297         int delta;
  298 
  299         if (poll_handlers == 0 || poll_shutting_down)
  300                 return;
  301 
  302         microuptime(&t);
  303         delta = (t.tv_usec - prev_t.tv_usec) +
  304                 (t.tv_sec - prev_t.tv_sec)*1000000;
  305         if (delta * hz < 500000)
  306                 short_ticks++;
  307         else
  308                 prev_t = t;
  309 
  310         if (pending_polls > 100) {
  311                 /*
  312                  * Too much, assume it has stalled (not always true
  313                  * see comment above).
  314                  */
  315                 stalled++;
  316                 pending_polls = 0;
  317                 phase = 0;
  318         }
  319 
  320         if (phase <= 2) {
  321                 if (phase != 0)
  322                         suspect++;
  323                 phase = 1;
  324                 netisr_poll_scheduled = 1;
  325                 netisr_pollmore_scheduled = 1;
  326                 netisr_sched_poll();
  327                 phase = 2;
  328         }
  329         if (pending_polls++ > 0)
  330                 lost_polls++;
  331 }
  332 
  333 /*
  334  * ether_poll is called from the idle loop.
  335  */
  336 static void
  337 ether_poll(int count)
  338 {
  339         struct epoch_tracker et;
  340         int i;
  341 
  342         mtx_lock(&poll_mtx);
  343 
  344         if (count > poll_each_burst)
  345                 count = poll_each_burst;
  346 
  347         NET_EPOCH_ENTER(et);
  348         for (i = 0 ; i < poll_handlers ; i++)
  349                 pr[i].handler(pr[i].ifp, POLL_ONLY, count);
  350         NET_EPOCH_EXIT(et);
  351 
  352         mtx_unlock(&poll_mtx);
  353 }
  354 
  355 /*
  356  * netisr_pollmore is called after other netisr's, possibly scheduling
  357  * another NETISR_POLL call, or adapting the burst size for the next cycle.
  358  *
  359  * It is very bad to fetch large bursts of packets from a single card at once,
  360  * because the burst could take a long time to be completely processed, or
  361  * could saturate the intermediate queue (ipintrq or similar) leading to
  362  * losses or unfairness. To reduce the problem, and also to account better for
  363  * time spent in network-related processing, we split the burst in smaller
  364  * chunks of fixed size, giving control to the other netisr's between chunks.
  365  * This helps in improving the fairness, reducing livelock (because we
  366  * emulate more closely the "process to completion" that we have with
  367  * fastforwarding) and accounting for the work performed in low level
  368  * handling and forwarding.
  369  */
  370 
  371 static struct timeval poll_start_t;
  372 
  373 void
  374 netisr_pollmore(void)
  375 {
  376         struct timeval t;
  377         int kern_load;
  378 
  379         if (poll_handlers == 0)
  380                 return;
  381 
  382         mtx_lock(&poll_mtx);
  383         if (!netisr_pollmore_scheduled) {
  384                 mtx_unlock(&poll_mtx);
  385                 return;
  386         }
  387         netisr_pollmore_scheduled = 0;
  388         phase = 5;
  389         if (residual_burst > 0) {
  390                 netisr_poll_scheduled = 1;
  391                 netisr_pollmore_scheduled = 1;
  392                 netisr_sched_poll();
  393                 mtx_unlock(&poll_mtx);
  394                 /* will run immediately on return, followed by netisrs */
  395                 return;
  396         }
  397         /* here we can account time spent in netisr's in this tick */
  398         microuptime(&t);
  399         kern_load = (t.tv_usec - poll_start_t.tv_usec) +
  400                 (t.tv_sec - poll_start_t.tv_sec)*1000000;       /* us */
  401         kern_load = (kern_load * hz) / 10000;                   /* 0..100 */
  402         if (kern_load > (100 - user_frac)) { /* try decrease ticks */
  403                 if (poll_burst > 1)
  404                         poll_burst--;
  405         } else {
  406                 if (poll_burst < poll_burst_max)
  407                         poll_burst++;
  408         }
  409 
  410         pending_polls--;
  411         if (pending_polls == 0) /* we are done */
  412                 phase = 0;
  413         else {
  414                 /*
  415                  * Last cycle was long and caused us to miss one or more
  416                  * hardclock ticks. Restart processing again, but slightly
  417                  * reduce the burst size to prevent that this happens again.
  418                  */
  419                 poll_burst -= (poll_burst / 8);
  420                 if (poll_burst < 1)
  421                         poll_burst = 1;
  422                 netisr_poll_scheduled = 1;
  423                 netisr_pollmore_scheduled = 1;
  424                 netisr_sched_poll();
  425                 phase = 6;
  426         }
  427         mtx_unlock(&poll_mtx);
  428 }
  429 
  430 /*
  431  * netisr_poll is typically scheduled once per tick.
  432  */
  433 void
  434 netisr_poll(void)
  435 {
  436         int i, cycles;
  437         enum poll_cmd arg = POLL_ONLY;
  438 
  439         NET_EPOCH_ASSERT();
  440 
  441         if (poll_handlers == 0)
  442                 return;
  443 
  444         mtx_lock(&poll_mtx);
  445         if (!netisr_poll_scheduled) {
  446                 mtx_unlock(&poll_mtx);
  447                 return;
  448         }
  449         netisr_poll_scheduled = 0;
  450         phase = 3;
  451         if (residual_burst == 0) { /* first call in this tick */
  452                 microuptime(&poll_start_t);
  453                 if (++reg_frac_count == reg_frac) {
  454                         arg = POLL_AND_CHECK_STATUS;
  455                         reg_frac_count = 0;
  456                 }
  457 
  458                 residual_burst = poll_burst;
  459         }
  460         cycles = (residual_burst < poll_each_burst) ?
  461                 residual_burst : poll_each_burst;
  462         residual_burst -= cycles;
  463 
  464         for (i = 0 ; i < poll_handlers ; i++)
  465                 pr[i].handler(pr[i].ifp, arg, cycles);
  466 
  467         phase = 4;
  468         mtx_unlock(&poll_mtx);
  469 }
  470 
  471 /*
  472  * Try to register routine for polling. Returns 0 if successful
  473  * (and polling should be enabled), error code otherwise.
  474  * A device is not supposed to register itself multiple times.
  475  *
  476  * This is called from within the *_ioctl() functions.
  477  */
  478 int
  479 ether_poll_register(poll_handler_t *h, if_t ifp)
  480 {
  481         int i;
  482 
  483         KASSERT(h != NULL, ("%s: handler is NULL", __func__));
  484         KASSERT(ifp != NULL, ("%s: ifp is NULL", __func__));
  485 
  486         mtx_lock(&poll_mtx);
  487         if (poll_handlers >= POLL_LIST_LEN) {
  488                 /*
  489                  * List full, cannot register more entries.
  490                  * This should never happen; if it does, it is probably a
  491                  * broken driver trying to register multiple times. Checking
  492                  * this at runtime is expensive, and won't solve the problem
  493                  * anyways, so just report a few times and then give up.
  494                  */
  495                 static int verbose = 10 ;
  496                 if (verbose >0) {
  497                         log(LOG_ERR, "poll handlers list full, "
  498                             "maybe a broken driver ?\n");
  499                         verbose--;
  500                 }
  501                 mtx_unlock(&poll_mtx);
  502                 return (ENOMEM); /* no polling for you */
  503         }
  504 
  505         for (i = 0 ; i < poll_handlers ; i++)
  506                 if (pr[i].ifp == ifp && pr[i].handler != NULL) {
  507                         mtx_unlock(&poll_mtx);
  508                         log(LOG_DEBUG, "ether_poll_register: %s: handler"
  509                             " already registered\n", ifp->if_xname);
  510                         return (EEXIST);
  511                 }
  512 
  513         pr[poll_handlers].handler = h;
  514         pr[poll_handlers].ifp = ifp;
  515         poll_handlers++;
  516         mtx_unlock(&poll_mtx);
  517         if (idlepoll_sleeping)
  518                 wakeup(&idlepoll_sleeping);
  519         return (0);
  520 }
  521 
  522 /*
  523  * Remove interface from the polling list. Called from *_ioctl(), too.
  524  */
  525 int
  526 ether_poll_deregister(if_t ifp)
  527 {
  528         int i;
  529 
  530         KASSERT(ifp != NULL, ("%s: ifp is NULL", __func__));
  531 
  532         mtx_lock(&poll_mtx);
  533 
  534         for (i = 0 ; i < poll_handlers ; i++)
  535                 if (pr[i].ifp == ifp) /* found it */
  536                         break;
  537         if (i == poll_handlers) {
  538                 log(LOG_DEBUG, "ether_poll_deregister: %s: not found!\n",
  539                     ifp->if_xname);
  540                 mtx_unlock(&poll_mtx);
  541                 return (ENOENT);
  542         }
  543         poll_handlers--;
  544         if (i < poll_handlers) { /* Last entry replaces this one. */
  545                 pr[i].handler = pr[poll_handlers].handler;
  546                 pr[i].ifp = pr[poll_handlers].ifp;
  547         }
  548         mtx_unlock(&poll_mtx);
  549         return (0);
  550 }
  551 
  552 static void
  553 poll_idle(void)
  554 {
  555         struct thread *td = curthread;
  556         struct rtprio rtp;
  557 
  558         rtp.prio = RTP_PRIO_MAX;        /* lowest priority */
  559         rtp.type = RTP_PRIO_IDLE;
  560         PROC_SLOCK(td->td_proc);
  561         rtp_to_pri(&rtp, td);
  562         PROC_SUNLOCK(td->td_proc);
  563 
  564         for (;;) {
  565                 if (poll_in_idle_loop && poll_handlers > 0) {
  566                         idlepoll_sleeping = 0;
  567                         ether_poll(poll_each_burst);
  568                         thread_lock(td);
  569                         mi_switch(SW_VOL);
  570                 } else {
  571                         idlepoll_sleeping = 1;
  572                         tsleep(&idlepoll_sleeping, 0, "pollid", hz * 3);
  573                 }
  574         }
  575 }
  576 
  577 static struct proc *idlepoll;
  578 static struct kproc_desc idlepoll_kp = {
  579          "idlepoll",
  580          poll_idle,
  581          &idlepoll
  582 };
  583 SYSINIT(idlepoll, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, kproc_start,
  584     &idlepoll_kp);

Cache object: 3ebe9c5ebd7d26db9672c847f2b6c6ab


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