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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("$FreeBSD$");
   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/socket.h>                 /* needed by net/if.h           */
   37 #include <sys/sockio.h>
   38 #include <sys/sysctl.h>
   39 #include <sys/syslog.h>
   40 
   41 #include <net/if.h>                     /* for IFF_* flags              */
   42 #include <net/netisr.h>                 /* for NETISR_POLL              */
   43 
   44 #include <sys/proc.h>
   45 #include <sys/resourcevar.h>
   46 #include <sys/kthread.h>
   47 
   48 static void netisr_poll(void);          /* the two netisr handlers      */
   49 static void netisr_pollmore(void);
   50 static int poll_switch(SYSCTL_HANDLER_ARGS);
   51 
   52 void hardclock_device_poll(void);       /* hook from hardclock          */
   53 void ether_poll(int);                   /* polling in idle loop         */
   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  *      0 <= poll_each_burst
   95  *      MIN_POLL_BURST_MAX <= poll_burst_max <= MAX_POLL_BURST_MAX
   96  */
   97 
   98 #define MIN_POLL_BURST_MAX      10
   99 #define MAX_POLL_BURST_MAX      1000
  100 
  101 static uint32_t poll_burst = 5;
  102 static uint32_t poll_burst_max = 150;   /* good for 100Mbit net and HZ=1000 */
  103 static uint32_t poll_each_burst = 5;
  104 
  105 SYSCTL_NODE(_kern, OID_AUTO, polling, CTLFLAG_RW, 0,
  106         "Device polling parameters");
  107 
  108 SYSCTL_UINT(_kern_polling, OID_AUTO, burst, CTLFLAG_RD,
  109         &poll_burst, 0, "Current polling burst size");
  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 int polling = 0;
  232 SYSCTL_PROC(_kern_polling, OID_AUTO, enable, CTLTYPE_UINT | CTLFLAG_RW,
  233         0, sizeof(int), poll_switch, "I", "Switch polling for all interfaces");
  234 
  235 static uint32_t phase;
  236 SYSCTL_UINT(_kern_polling, OID_AUTO, phase, CTLFLAG_RD,
  237         &phase, 0, "Polling phase");
  238 
  239 static uint32_t suspect;
  240 SYSCTL_UINT(_kern_polling, OID_AUTO, suspect, CTLFLAG_RD,
  241         &suspect, 0, "suspect event");
  242 
  243 static uint32_t stalled;
  244 SYSCTL_UINT(_kern_polling, OID_AUTO, stalled, CTLFLAG_RD,
  245         &stalled, 0, "potential stalls");
  246 
  247 static uint32_t idlepoll_sleeping; /* idlepoll is sleeping */
  248 SYSCTL_UINT(_kern_polling, OID_AUTO, idlepoll_sleeping, CTLFLAG_RD,
  249         &idlepoll_sleeping, 0, "idlepoll is sleeping");
  250 
  251 
  252 #define POLL_LIST_LEN  128
  253 struct pollrec {
  254         poll_handler_t  *handler;
  255         struct ifnet    *ifp;
  256 };
  257 
  258 static struct pollrec pr[POLL_LIST_LEN];
  259 
  260 static void
  261 init_device_poll(void)
  262 {
  263 
  264         mtx_init(&poll_mtx, "polling", NULL, MTX_DEF);
  265         netisr_register(NETISR_POLL, (netisr_t *)netisr_poll, NULL,
  266             NETISR_MPSAFE);
  267         netisr_register(NETISR_POLLMORE, (netisr_t *)netisr_pollmore, NULL,
  268             NETISR_MPSAFE);
  269 }
  270 SYSINIT(device_poll, SI_SUB_CLOCKS, SI_ORDER_MIDDLE, init_device_poll, NULL);
  271 
  272 
  273 /*
  274  * Hook from hardclock. Tries to schedule a netisr, but keeps track
  275  * of lost ticks due to the previous handler taking too long.
  276  * Normally, this should not happen, because polling handler should
  277  * run for a short time. However, in some cases (e.g. when there are
  278  * changes in link status etc.) the drivers take a very long time
  279  * (even in the order of milliseconds) to reset and reconfigure the
  280  * device, causing apparent lost polls.
  281  *
  282  * The first part of the code is just for debugging purposes, and tries
  283  * to count how often hardclock ticks are shorter than they should,
  284  * meaning either stray interrupts or delayed events.
  285  */
  286 void
  287 hardclock_device_poll(void)
  288 {
  289         static struct timeval prev_t, t;
  290         int delta;
  291 
  292         if (poll_handlers == 0)
  293                 return;
  294 
  295         microuptime(&t);
  296         delta = (t.tv_usec - prev_t.tv_usec) +
  297                 (t.tv_sec - prev_t.tv_sec)*1000000;
  298         if (delta * hz < 500000)
  299                 short_ticks++;
  300         else
  301                 prev_t = t;
  302 
  303         if (pending_polls > 100) {
  304                 /*
  305                  * Too much, assume it has stalled (not always true
  306                  * see comment above).
  307                  */
  308                 stalled++;
  309                 pending_polls = 0;
  310                 phase = 0;
  311         }
  312 
  313         if (phase <= 2) {
  314                 if (phase != 0)
  315                         suspect++;
  316                 phase = 1;
  317                 schednetisrbits(1 << NETISR_POLL | 1 << NETISR_POLLMORE);
  318                 phase = 2;
  319         }
  320         if (pending_polls++ > 0)
  321                 lost_polls++;
  322 }
  323 
  324 /*
  325  * ether_poll is called from the idle loop.
  326  */
  327 void
  328 ether_poll(int count)
  329 {
  330         int i;
  331 
  332         mtx_lock(&poll_mtx);
  333 
  334         if (count > poll_each_burst)
  335                 count = poll_each_burst;
  336 
  337         for (i = 0 ; i < poll_handlers ; i++)
  338                 pr[i].handler(pr[i].ifp, POLL_ONLY, count);
  339 
  340         mtx_unlock(&poll_mtx);
  341 }
  342 
  343 /*
  344  * netisr_pollmore is called after other netisr's, possibly scheduling
  345  * another NETISR_POLL call, or adapting the burst size for the next cycle.
  346  *
  347  * It is very bad to fetch large bursts of packets from a single card at once,
  348  * because the burst could take a long time to be completely processed, or
  349  * could saturate the intermediate queue (ipintrq or similar) leading to
  350  * losses or unfairness. To reduce the problem, and also to account better for
  351  * time spent in network-related processing, we split the burst in smaller
  352  * chunks of fixed size, giving control to the other netisr's between chunks.
  353  * This helps in improving the fairness, reducing livelock (because we
  354  * emulate more closely the "process to completion" that we have with
  355  * fastforwarding) and accounting for the work performed in low level
  356  * handling and forwarding.
  357  */
  358 
  359 static struct timeval poll_start_t;
  360 
  361 void
  362 netisr_pollmore()
  363 {
  364         struct timeval t;
  365         int kern_load;
  366 
  367         mtx_lock(&poll_mtx);
  368         phase = 5;
  369         if (residual_burst > 0) {
  370                 schednetisrbits(1 << NETISR_POLL | 1 << NETISR_POLLMORE);
  371                 mtx_unlock(&poll_mtx);
  372                 /* will run immediately on return, followed by netisrs */
  373                 return;
  374         }
  375         /* here we can account time spent in netisr's in this tick */
  376         microuptime(&t);
  377         kern_load = (t.tv_usec - poll_start_t.tv_usec) +
  378                 (t.tv_sec - poll_start_t.tv_sec)*1000000;       /* us */
  379         kern_load = (kern_load * hz) / 10000;                   /* 0..100 */
  380         if (kern_load > (100 - user_frac)) { /* try decrease ticks */
  381                 if (poll_burst > 1)
  382                         poll_burst--;
  383         } else {
  384                 if (poll_burst < poll_burst_max)
  385                         poll_burst++;
  386         }
  387 
  388         pending_polls--;
  389         if (pending_polls == 0) /* we are done */
  390                 phase = 0;
  391         else {
  392                 /*
  393                  * Last cycle was long and caused us to miss one or more
  394                  * hardclock ticks. Restart processing again, but slightly
  395                  * reduce the burst size to prevent that this happens again.
  396                  */
  397                 poll_burst -= (poll_burst / 8);
  398                 if (poll_burst < 1)
  399                         poll_burst = 1;
  400                 schednetisrbits(1 << NETISR_POLL | 1 << NETISR_POLLMORE);
  401                 phase = 6;
  402         }
  403         mtx_unlock(&poll_mtx);
  404 }
  405 
  406 /*
  407  * netisr_poll is scheduled by schednetisr when appropriate, typically once
  408  * per tick.
  409  */
  410 static void
  411 netisr_poll(void)
  412 {
  413         int i, cycles;
  414         enum poll_cmd arg = POLL_ONLY;
  415 
  416         mtx_lock(&poll_mtx);
  417         phase = 3;
  418         if (residual_burst == 0) { /* first call in this tick */
  419                 microuptime(&poll_start_t);
  420                 if (++reg_frac_count == reg_frac) {
  421                         arg = POLL_AND_CHECK_STATUS;
  422                         reg_frac_count = 0;
  423                 }
  424 
  425                 residual_burst = poll_burst;
  426         }
  427         cycles = (residual_burst < poll_each_burst) ?
  428                 residual_burst : poll_each_burst;
  429         residual_burst -= cycles;
  430 
  431         for (i = 0 ; i < poll_handlers ; i++)
  432                 pr[i].handler(pr[i].ifp, arg, cycles);
  433 
  434         phase = 4;
  435         mtx_unlock(&poll_mtx);
  436 }
  437 
  438 /*
  439  * Try to register routine for polling. Returns 0 if successful
  440  * (and polling should be enabled), error code otherwise.
  441  * A device is not supposed to register itself multiple times.
  442  *
  443  * This is called from within the *_ioctl() functions.
  444  */
  445 int
  446 ether_poll_register(poll_handler_t *h, struct ifnet *ifp)
  447 {
  448         int i;
  449 
  450         KASSERT(h != NULL, ("%s: handler is NULL", __func__));
  451         KASSERT(ifp != NULL, ("%s: ifp is NULL", __func__));
  452 
  453         mtx_lock(&poll_mtx);
  454         if (poll_handlers >= POLL_LIST_LEN) {
  455                 /*
  456                  * List full, cannot register more entries.
  457                  * This should never happen; if it does, it is probably a
  458                  * broken driver trying to register multiple times. Checking
  459                  * this at runtime is expensive, and won't solve the problem
  460                  * anyways, so just report a few times and then give up.
  461                  */
  462                 static int verbose = 10 ;
  463                 if (verbose >0) {
  464                         log(LOG_ERR, "poll handlers list full, "
  465                             "maybe a broken driver ?\n");
  466                         verbose--;
  467                 }
  468                 mtx_unlock(&poll_mtx);
  469                 return (ENOMEM); /* no polling for you */
  470         }
  471 
  472         for (i = 0 ; i < poll_handlers ; i++)
  473                 if (pr[i].ifp == ifp && pr[i].handler != NULL) {
  474                         mtx_unlock(&poll_mtx);
  475                         log(LOG_DEBUG, "ether_poll_register: %s: handler"
  476                             " already registered\n", ifp->if_xname);
  477                         return (EEXIST);
  478                 }
  479 
  480         pr[poll_handlers].handler = h;
  481         pr[poll_handlers].ifp = ifp;
  482         poll_handlers++;
  483         mtx_unlock(&poll_mtx);
  484         if (idlepoll_sleeping)
  485                 wakeup(&idlepoll_sleeping);
  486         return (0);
  487 }
  488 
  489 /*
  490  * Remove interface from the polling list. Called from *_ioctl(), too.
  491  */
  492 int
  493 ether_poll_deregister(struct ifnet *ifp)
  494 {
  495         int i;
  496 
  497         KASSERT(ifp != NULL, ("%s: ifp is NULL", __func__));
  498 
  499         mtx_lock(&poll_mtx);
  500 
  501         for (i = 0 ; i < poll_handlers ; i++)
  502                 if (pr[i].ifp == ifp) /* found it */
  503                         break;
  504         if (i == poll_handlers) {
  505                 log(LOG_DEBUG, "ether_poll_deregister: %s: not found!\n",
  506                     ifp->if_xname);
  507                 mtx_unlock(&poll_mtx);
  508                 return (ENOENT);
  509         }
  510         poll_handlers--;
  511         if (i < poll_handlers) { /* Last entry replaces this one. */
  512                 pr[i].handler = pr[poll_handlers].handler;
  513                 pr[i].ifp = pr[poll_handlers].ifp;
  514         }
  515         mtx_unlock(&poll_mtx);
  516         return (0);
  517 }
  518 
  519 /*
  520  * Legacy interface for turning polling on all interfaces at one time.
  521  */
  522 static int
  523 poll_switch(SYSCTL_HANDLER_ARGS)
  524 {
  525         struct ifnet *ifp;
  526         int error;
  527         int val = polling;
  528 
  529         error = sysctl_handle_int(oidp, &val, 0, req);
  530         if (error || !req->newptr )
  531                 return (error);
  532 
  533         if (val == polling)
  534                 return (0);
  535 
  536         if (val < 0 || val > 1)
  537                 return (EINVAL);
  538 
  539         polling = val;
  540 
  541         IFNET_RLOCK();
  542         TAILQ_FOREACH(ifp, &ifnet, if_link) {
  543                 if (ifp->if_capabilities & IFCAP_POLLING) {
  544                         struct ifreq ifr;
  545 
  546                         if (val == 1)
  547                                 ifr.ifr_reqcap =
  548                                     ifp->if_capenable | IFCAP_POLLING;
  549                         else
  550                                 ifr.ifr_reqcap =
  551                                     ifp->if_capenable & ~IFCAP_POLLING;
  552                         IFF_LOCKGIANT(ifp);     /* LOR here */
  553                         (void) (*ifp->if_ioctl)(ifp, SIOCSIFCAP, (caddr_t)&ifr);
  554                         IFF_UNLOCKGIANT(ifp);
  555                 }
  556         }
  557         IFNET_RUNLOCK();
  558 
  559         log(LOG_ERR, "kern.polling.enable is deprecated. Use ifconfig(8)");
  560 
  561         return (0);
  562 }
  563 
  564 static void
  565 poll_idle(void)
  566 {
  567         struct thread *td = curthread;
  568         struct rtprio rtp;
  569 
  570         rtp.prio = RTP_PRIO_MAX;        /* lowest priority */
  571         rtp.type = RTP_PRIO_IDLE;
  572         PROC_SLOCK(td->td_proc);
  573         rtp_to_pri(&rtp, td);
  574         PROC_SUNLOCK(td->td_proc);
  575 
  576         for (;;) {
  577                 if (poll_in_idle_loop && poll_handlers > 0) {
  578                         idlepoll_sleeping = 0;
  579                         ether_poll(poll_each_burst);
  580                         thread_lock(td);
  581                         mi_switch(SW_VOL, NULL);
  582                         thread_unlock(td);
  583                 } else {
  584                         idlepoll_sleeping = 1;
  585                         tsleep(&idlepoll_sleeping, 0, "pollid", hz * 3);
  586                 }
  587         }
  588 }
  589 
  590 static struct proc *idlepoll;
  591 static struct kproc_desc idlepoll_kp = {
  592          "idlepoll",
  593          poll_idle,
  594          &idlepoll
  595 };
  596 SYSINIT(idlepoll, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, kproc_start,
  597     &idlepoll_kp);

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