The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: 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  * Copyright (c) 2001-2002 Luigi Rizzo
    3  *
    4  * Supported by: the Xorp Project (www.xorp.org)
    5  *
    6  * Redistribution and use in source and binary forms, with or without
    7  * modification, are permitted provided that the following conditions
    8  * are met:
    9  * 1. Redistributions of source code must retain the above copyright
   10  *    notice, this list of conditions and the following disclaimer.
   11  * 2. Redistributions in binary form must reproduce the above copyright
   12  *    notice, this list of conditions and the following disclaimer in the
   13  *    documentation and/or other materials provided with the distribution.
   14  *
   15  * THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
   16  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   17  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   18  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
   19  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   20  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   21  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   22  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   23  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   24  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   25  * SUCH DAMAGE.
   26  */
   27 
   28 #include <sys/cdefs.h>
   29 __FBSDID("$FreeBSD: releng/9.0/sys/kern/kern_poll.c 196267 2009-08-15 23:07:43Z rwatson $");
   30 
   31 #include "opt_device_polling.h"
   32 
   33 #include <sys/param.h>
   34 #include <sys/systm.h>
   35 #include <sys/kernel.h>
   36 #include <sys/kthread.h>
   37 #include <sys/proc.h>
   38 #include <sys/eventhandler.h>
   39 #include <sys/resourcevar.h>
   40 #include <sys/socket.h>                 /* needed by net/if.h           */
   41 #include <sys/sockio.h>
   42 #include <sys/sysctl.h>
   43 #include <sys/syslog.h>
   44 
   45 #include <net/if.h>                     /* for IFF_* flags              */
   46 #include <net/netisr.h>                 /* for NETISR_POLL              */
   47 #include <net/vnet.h>
   48 
   49 void hardclock_device_poll(void);       /* hook from hardclock          */
   50 
   51 static struct mtx       poll_mtx;
   52 
   53 /*
   54  * Polling support for [network] device drivers.
   55  *
   56  * Drivers which support this feature can register with the
   57  * polling code.
   58  *
   59  * If registration is successful, the driver must disable interrupts,
   60  * and further I/O is performed through the handler, which is invoked
   61  * (at least once per clock tick) with 3 arguments: the "arg" passed at
   62  * register time (a struct ifnet pointer), a command, and a "count" limit.
   63  *
   64  * The command can be one of the following:
   65  *  POLL_ONLY: quick move of "count" packets from input/output queues.
   66  *  POLL_AND_CHECK_STATUS: as above, plus check status registers or do
   67  *      other more expensive operations. This command is issued periodically
   68  *      but less frequently than POLL_ONLY.
   69  *
   70  * The count limit specifies how much work the handler can do during the
   71  * call -- typically this is the number of packets to be received, or
   72  * transmitted, etc. (drivers are free to interpret this number, as long
   73  * as the max time spent in the function grows roughly linearly with the
   74  * count).
   75  *
   76  * Polling is enabled and disabled via setting IFCAP_POLLING flag on
   77  * the interface. The driver ioctl handler should register interface
   78  * with polling and disable interrupts, if registration was successful.
   79  *
   80  * A second variable controls the sharing of CPU between polling/kernel
   81  * network processing, and other activities (typically userlevel tasks):
   82  * kern.polling.user_frac (between 0 and 100, default 50) sets the share
   83  * of CPU allocated to user tasks. CPU is allocated proportionally to the
   84  * shares, by dynamically adjusting the "count" (poll_burst).
   85  *
   86  * Other parameters can should be left to their default values.
   87  * The following constraints hold
   88  *
   89  *      1 <= poll_each_burst <= poll_burst <= poll_burst_max
   90  *      0 <= poll_each_burst
   91  *      MIN_POLL_BURST_MAX <= poll_burst_max <= MAX_POLL_BURST_MAX
   92  */
   93 
   94 #define MIN_POLL_BURST_MAX      10
   95 #define MAX_POLL_BURST_MAX      1000
   96 
   97 static uint32_t poll_burst = 5;
   98 static uint32_t poll_burst_max = 150;   /* good for 100Mbit net and HZ=1000 */
   99 static uint32_t poll_each_burst = 5;
  100 
  101 SYSCTL_NODE(_kern, OID_AUTO, polling, CTLFLAG_RW, 0,
  102         "Device polling parameters");
  103 
  104 SYSCTL_UINT(_kern_polling, OID_AUTO, burst, CTLFLAG_RD,
  105         &poll_burst, 0, "Current polling burst size");
  106 
  107 static int      netisr_poll_scheduled;
  108 static int      netisr_pollmore_scheduled;
  109 static int      poll_shutting_down;
  110 
  111 static int poll_burst_max_sysctl(SYSCTL_HANDLER_ARGS)
  112 {
  113         uint32_t val = poll_burst_max;
  114         int error;
  115 
  116         error = sysctl_handle_int(oidp, &val, 0, req);
  117         if (error || !req->newptr )
  118                 return (error);
  119         if (val < MIN_POLL_BURST_MAX || val > MAX_POLL_BURST_MAX)
  120                 return (EINVAL);
  121 
  122         mtx_lock(&poll_mtx);
  123         poll_burst_max = val;
  124         if (poll_burst > poll_burst_max)
  125                 poll_burst = poll_burst_max;
  126         if (poll_each_burst > poll_burst_max)
  127                 poll_each_burst = MIN_POLL_BURST_MAX;
  128         mtx_unlock(&poll_mtx);
  129 
  130         return (0);
  131 }
  132 SYSCTL_PROC(_kern_polling, OID_AUTO, burst_max, CTLTYPE_UINT | CTLFLAG_RW,
  133         0, sizeof(uint32_t), poll_burst_max_sysctl, "I", "Max Polling burst size");
  134 
  135 static int poll_each_burst_sysctl(SYSCTL_HANDLER_ARGS)
  136 {
  137         uint32_t val = poll_each_burst;
  138         int error;
  139 
  140         error = sysctl_handle_int(oidp, &val, 0, req);
  141         if (error || !req->newptr )
  142                 return (error);
  143         if (val < 1)
  144                 return (EINVAL);
  145 
  146         mtx_lock(&poll_mtx);
  147         if (val > poll_burst_max) {
  148                 mtx_unlock(&poll_mtx);
  149                 return (EINVAL);
  150         }
  151         poll_each_burst = val;
  152         mtx_unlock(&poll_mtx);
  153 
  154         return (0);
  155 }
  156 SYSCTL_PROC(_kern_polling, OID_AUTO, each_burst, CTLTYPE_UINT | CTLFLAG_RW,
  157         0, sizeof(uint32_t), poll_each_burst_sysctl, "I",
  158         "Max size of each burst");
  159 
  160 static uint32_t poll_in_idle_loop=0;    /* do we poll in idle loop ? */
  161 SYSCTL_UINT(_kern_polling, OID_AUTO, idle_poll, CTLFLAG_RW,
  162         &poll_in_idle_loop, 0, "Enable device polling in idle loop");
  163 
  164 static uint32_t user_frac = 50;
  165 static int user_frac_sysctl(SYSCTL_HANDLER_ARGS)
  166 {
  167         uint32_t val = user_frac;
  168         int error;
  169 
  170         error = sysctl_handle_int(oidp, &val, 0, req);
  171         if (error || !req->newptr )
  172                 return (error);
  173         if (val < 0 || val > 99)
  174                 return (EINVAL);
  175 
  176         mtx_lock(&poll_mtx);
  177         user_frac = val;
  178         mtx_unlock(&poll_mtx);
  179 
  180         return (0);
  181 }
  182 SYSCTL_PROC(_kern_polling, OID_AUTO, user_frac, CTLTYPE_UINT | CTLFLAG_RW,
  183         0, sizeof(uint32_t), user_frac_sysctl, "I",
  184         "Desired user fraction of cpu time");
  185 
  186 static uint32_t reg_frac_count = 0;
  187 static uint32_t reg_frac = 20 ;
  188 static int reg_frac_sysctl(SYSCTL_HANDLER_ARGS)
  189 {
  190         uint32_t val = reg_frac;
  191         int error;
  192 
  193         error = sysctl_handle_int(oidp, &val, 0, req);
  194         if (error || !req->newptr )
  195                 return (error);
  196         if (val < 1 || val > hz)
  197                 return (EINVAL);
  198 
  199         mtx_lock(&poll_mtx);
  200         reg_frac = val;
  201         if (reg_frac_count >= reg_frac)
  202                 reg_frac_count = 0;
  203         mtx_unlock(&poll_mtx);
  204 
  205         return (0);
  206 }
  207 SYSCTL_PROC(_kern_polling, OID_AUTO, reg_frac, CTLTYPE_UINT | CTLFLAG_RW,
  208         0, sizeof(uint32_t), reg_frac_sysctl, "I",
  209         "Every this many cycles check registers");
  210 
  211 static uint32_t short_ticks;
  212 SYSCTL_UINT(_kern_polling, OID_AUTO, short_ticks, CTLFLAG_RD,
  213         &short_ticks, 0, "Hardclock ticks shorter than they should be");
  214 
  215 static uint32_t lost_polls;
  216 SYSCTL_UINT(_kern_polling, OID_AUTO, lost_polls, CTLFLAG_RD,
  217         &lost_polls, 0, "How many times we would have lost a poll tick");
  218 
  219 static uint32_t pending_polls;
  220 SYSCTL_UINT(_kern_polling, OID_AUTO, pending_polls, CTLFLAG_RD,
  221         &pending_polls, 0, "Do we need to poll again");
  222 
  223 static int residual_burst = 0;
  224 SYSCTL_INT(_kern_polling, OID_AUTO, residual_burst, CTLFLAG_RD,
  225         &residual_burst, 0, "# of residual cycles in burst");
  226 
  227 static uint32_t poll_handlers; /* next free entry in pr[]. */
  228 SYSCTL_UINT(_kern_polling, OID_AUTO, handlers, CTLFLAG_RD,
  229         &poll_handlers, 0, "Number of registered poll handlers");
  230 
  231 static uint32_t phase;
  232 SYSCTL_UINT(_kern_polling, OID_AUTO, phase, CTLFLAG_RD,
  233         &phase, 0, "Polling phase");
  234 
  235 static uint32_t suspect;
  236 SYSCTL_UINT(_kern_polling, OID_AUTO, suspect, CTLFLAG_RD,
  237         &suspect, 0, "suspect event");
  238 
  239 static uint32_t stalled;
  240 SYSCTL_UINT(_kern_polling, OID_AUTO, stalled, CTLFLAG_RD,
  241         &stalled, 0, "potential stalls");
  242 
  243 static uint32_t idlepoll_sleeping; /* idlepoll is sleeping */
  244 SYSCTL_UINT(_kern_polling, OID_AUTO, idlepoll_sleeping, CTLFLAG_RD,
  245         &idlepoll_sleeping, 0, "idlepoll is sleeping");
  246 
  247 
  248 #define POLL_LIST_LEN  128
  249 struct pollrec {
  250         poll_handler_t  *handler;
  251         struct ifnet    *ifp;
  252 };
  253 
  254 static struct pollrec pr[POLL_LIST_LEN];
  255 
  256 static void
  257 poll_shutdown(void *arg, int howto)
  258 {
  259 
  260         poll_shutting_down = 1;
  261 }
  262 
  263 static void
  264 init_device_poll(void)
  265 {
  266 
  267         mtx_init(&poll_mtx, "polling", NULL, MTX_DEF);
  268         EVENTHANDLER_REGISTER(shutdown_post_sync, poll_shutdown, NULL,
  269             SHUTDOWN_PRI_LAST);
  270 }
  271 SYSINIT(device_poll, SI_SUB_CLOCKS, SI_ORDER_MIDDLE, init_device_poll, NULL);
  272 
  273 
  274 /*
  275  * Hook from hardclock. Tries to schedule a netisr, but keeps track
  276  * of lost ticks due to the previous handler taking too long.
  277  * Normally, this should not happen, because polling handler should
  278  * run for a short time. However, in some cases (e.g. when there are
  279  * changes in link status etc.) the drivers take a very long time
  280  * (even in the order of milliseconds) to reset and reconfigure the
  281  * device, causing apparent lost polls.
  282  *
  283  * The first part of the code is just for debugging purposes, and tries
  284  * to count how often hardclock ticks are shorter than they should,
  285  * meaning either stray interrupts or delayed events.
  286  */
  287 void
  288 hardclock_device_poll(void)
  289 {
  290         static struct timeval prev_t, t;
  291         int delta;
  292 
  293         if (poll_handlers == 0 || poll_shutting_down)
  294                 return;
  295 
  296         microuptime(&t);
  297         delta = (t.tv_usec - prev_t.tv_usec) +
  298                 (t.tv_sec - prev_t.tv_sec)*1000000;
  299         if (delta * hz < 500000)
  300                 short_ticks++;
  301         else
  302                 prev_t = t;
  303 
  304         if (pending_polls > 100) {
  305                 /*
  306                  * Too much, assume it has stalled (not always true
  307                  * see comment above).
  308                  */
  309                 stalled++;
  310                 pending_polls = 0;
  311                 phase = 0;
  312         }
  313 
  314         if (phase <= 2) {
  315                 if (phase != 0)
  316                         suspect++;
  317                 phase = 1;
  318                 netisr_poll_scheduled = 1;
  319                 netisr_pollmore_scheduled = 1;
  320                 netisr_sched_poll();
  321                 phase = 2;
  322         }
  323         if (pending_polls++ > 0)
  324                 lost_polls++;
  325 }
  326 
  327 /*
  328  * ether_poll is called from the idle loop.
  329  */
  330 static void
  331 ether_poll(int count)
  332 {
  333         int i;
  334 
  335         mtx_lock(&poll_mtx);
  336 
  337         if (count > poll_each_burst)
  338                 count = poll_each_burst;
  339 
  340         for (i = 0 ; i < poll_handlers ; i++)
  341                 pr[i].handler(pr[i].ifp, POLL_ONLY, count);
  342 
  343         mtx_unlock(&poll_mtx);
  344 }
  345 
  346 /*
  347  * netisr_pollmore is called after other netisr's, possibly scheduling
  348  * another NETISR_POLL call, or adapting the burst size for the next cycle.
  349  *
  350  * It is very bad to fetch large bursts of packets from a single card at once,
  351  * because the burst could take a long time to be completely processed, or
  352  * could saturate the intermediate queue (ipintrq or similar) leading to
  353  * losses or unfairness. To reduce the problem, and also to account better for
  354  * time spent in network-related processing, we split the burst in smaller
  355  * chunks of fixed size, giving control to the other netisr's between chunks.
  356  * This helps in improving the fairness, reducing livelock (because we
  357  * emulate more closely the "process to completion" that we have with
  358  * fastforwarding) and accounting for the work performed in low level
  359  * handling and forwarding.
  360  */
  361 
  362 static struct timeval poll_start_t;
  363 
  364 void
  365 netisr_pollmore()
  366 {
  367         struct timeval t;
  368         int kern_load;
  369 
  370         mtx_lock(&poll_mtx);
  371         if (!netisr_pollmore_scheduled) {
  372                 mtx_unlock(&poll_mtx);
  373                 return;
  374         }
  375         netisr_pollmore_scheduled = 0;
  376         phase = 5;
  377         if (residual_burst > 0) {
  378                 netisr_poll_scheduled = 1;
  379                 netisr_pollmore_scheduled = 1;
  380                 netisr_sched_poll();
  381                 mtx_unlock(&poll_mtx);
  382                 /* will run immediately on return, followed by netisrs */
  383                 return;
  384         }
  385         /* here we can account time spent in netisr's in this tick */
  386         microuptime(&t);
  387         kern_load = (t.tv_usec - poll_start_t.tv_usec) +
  388                 (t.tv_sec - poll_start_t.tv_sec)*1000000;       /* us */
  389         kern_load = (kern_load * hz) / 10000;                   /* 0..100 */
  390         if (kern_load > (100 - user_frac)) { /* try decrease ticks */
  391                 if (poll_burst > 1)
  392                         poll_burst--;
  393         } else {
  394                 if (poll_burst < poll_burst_max)
  395                         poll_burst++;
  396         }
  397 
  398         pending_polls--;
  399         if (pending_polls == 0) /* we are done */
  400                 phase = 0;
  401         else {
  402                 /*
  403                  * Last cycle was long and caused us to miss one or more
  404                  * hardclock ticks. Restart processing again, but slightly
  405                  * reduce the burst size to prevent that this happens again.
  406                  */
  407                 poll_burst -= (poll_burst / 8);
  408                 if (poll_burst < 1)
  409                         poll_burst = 1;
  410                 netisr_poll_scheduled = 1;
  411                 netisr_pollmore_scheduled = 1;
  412                 netisr_sched_poll();
  413                 phase = 6;
  414         }
  415         mtx_unlock(&poll_mtx);
  416 }
  417 
  418 /*
  419  * netisr_poll is typically scheduled once per tick.
  420  */
  421 void
  422 netisr_poll(void)
  423 {
  424         int i, cycles;
  425         enum poll_cmd arg = POLL_ONLY;
  426 
  427         mtx_lock(&poll_mtx);
  428         if (!netisr_poll_scheduled) {
  429                 mtx_unlock(&poll_mtx);
  430                 return;
  431         }
  432         netisr_poll_scheduled = 0;
  433         phase = 3;
  434         if (residual_burst == 0) { /* first call in this tick */
  435                 microuptime(&poll_start_t);
  436                 if (++reg_frac_count == reg_frac) {
  437                         arg = POLL_AND_CHECK_STATUS;
  438                         reg_frac_count = 0;
  439                 }
  440 
  441                 residual_burst = poll_burst;
  442         }
  443         cycles = (residual_burst < poll_each_burst) ?
  444                 residual_burst : poll_each_burst;
  445         residual_burst -= cycles;
  446 
  447         for (i = 0 ; i < poll_handlers ; i++)
  448                 pr[i].handler(pr[i].ifp, arg, cycles);
  449 
  450         phase = 4;
  451         mtx_unlock(&poll_mtx);
  452 }
  453 
  454 /*
  455  * Try to register routine for polling. Returns 0 if successful
  456  * (and polling should be enabled), error code otherwise.
  457  * A device is not supposed to register itself multiple times.
  458  *
  459  * This is called from within the *_ioctl() functions.
  460  */
  461 int
  462 ether_poll_register(poll_handler_t *h, struct ifnet *ifp)
  463 {
  464         int i;
  465 
  466         KASSERT(h != NULL, ("%s: handler is NULL", __func__));
  467         KASSERT(ifp != NULL, ("%s: ifp is NULL", __func__));
  468 
  469         mtx_lock(&poll_mtx);
  470         if (poll_handlers >= POLL_LIST_LEN) {
  471                 /*
  472                  * List full, cannot register more entries.
  473                  * This should never happen; if it does, it is probably a
  474                  * broken driver trying to register multiple times. Checking
  475                  * this at runtime is expensive, and won't solve the problem
  476                  * anyways, so just report a few times and then give up.
  477                  */
  478                 static int verbose = 10 ;
  479                 if (verbose >0) {
  480                         log(LOG_ERR, "poll handlers list full, "
  481                             "maybe a broken driver ?\n");
  482                         verbose--;
  483                 }
  484                 mtx_unlock(&poll_mtx);
  485                 return (ENOMEM); /* no polling for you */
  486         }
  487 
  488         for (i = 0 ; i < poll_handlers ; i++)
  489                 if (pr[i].ifp == ifp && pr[i].handler != NULL) {
  490                         mtx_unlock(&poll_mtx);
  491                         log(LOG_DEBUG, "ether_poll_register: %s: handler"
  492                             " already registered\n", ifp->if_xname);
  493                         return (EEXIST);
  494                 }
  495 
  496         pr[poll_handlers].handler = h;
  497         pr[poll_handlers].ifp = ifp;
  498         poll_handlers++;
  499         mtx_unlock(&poll_mtx);
  500         if (idlepoll_sleeping)
  501                 wakeup(&idlepoll_sleeping);
  502         return (0);
  503 }
  504 
  505 /*
  506  * Remove interface from the polling list. Called from *_ioctl(), too.
  507  */
  508 int
  509 ether_poll_deregister(struct ifnet *ifp)
  510 {
  511         int i;
  512 
  513         KASSERT(ifp != NULL, ("%s: ifp is NULL", __func__));
  514 
  515         mtx_lock(&poll_mtx);
  516 
  517         for (i = 0 ; i < poll_handlers ; i++)
  518                 if (pr[i].ifp == ifp) /* found it */
  519                         break;
  520         if (i == poll_handlers) {
  521                 log(LOG_DEBUG, "ether_poll_deregister: %s: not found!\n",
  522                     ifp->if_xname);
  523                 mtx_unlock(&poll_mtx);
  524                 return (ENOENT);
  525         }
  526         poll_handlers--;
  527         if (i < poll_handlers) { /* Last entry replaces this one. */
  528                 pr[i].handler = pr[poll_handlers].handler;
  529                 pr[i].ifp = pr[poll_handlers].ifp;
  530         }
  531         mtx_unlock(&poll_mtx);
  532         return (0);
  533 }
  534 
  535 static void
  536 poll_idle(void)
  537 {
  538         struct thread *td = curthread;
  539         struct rtprio rtp;
  540 
  541         rtp.prio = RTP_PRIO_MAX;        /* lowest priority */
  542         rtp.type = RTP_PRIO_IDLE;
  543         PROC_SLOCK(td->td_proc);
  544         rtp_to_pri(&rtp, td);
  545         PROC_SUNLOCK(td->td_proc);
  546 
  547         for (;;) {
  548                 if (poll_in_idle_loop && poll_handlers > 0) {
  549                         idlepoll_sleeping = 0;
  550                         ether_poll(poll_each_burst);
  551                         thread_lock(td);
  552                         mi_switch(SW_VOL, NULL);
  553                         thread_unlock(td);
  554                 } else {
  555                         idlepoll_sleeping = 1;
  556                         tsleep(&idlepoll_sleeping, 0, "pollid", hz * 3);
  557                 }
  558         }
  559 }
  560 
  561 static struct proc *idlepoll;
  562 static struct kproc_desc idlepoll_kp = {
  563          "idlepoll",
  564          poll_idle,
  565          &idlepoll
  566 };
  567 SYSINIT(idlepoll, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, kproc_start,
  568     &idlepoll_kp);

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