FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_poll.c

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2001-2002 Luigi Rizzo
      *
      * Supported by: the Xorp Project (www.xorp.org)
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include "opt_device_polling.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/kthread.h>
    #include <sys/proc.h>
    #include <sys/eventhandler.h>
    #include <sys/resourcevar.h>
    #include <sys/socket.h>                 /* needed by net/if.h           */
    #include <sys/sockio.h>
    #include <sys/sysctl.h>
    #include <sys/syslog.h>
    
    #include <net/if.h>
    #include <net/if_var.h>
    #include <net/netisr.h>                 /* for NETISR_POLL              */
    #include <net/vnet.h>
    
    void hardclock_device_poll(void);       /* hook from hardclock          */
    
    static struct mtx       poll_mtx;
    
    /*
     * Polling support for [network] device drivers.
     *
     * Drivers which support this feature can register with the
     * polling code.
     *
     * If registration is successful, the driver must disable interrupts,
     * and further I/O is performed through the handler, which is invoked
     * (at least once per clock tick) with 3 arguments: the "arg" passed at
     * register time (a struct ifnet pointer), a command, and a "count" limit.
     *
     * The command can be one of the following:
     *  POLL_ONLY: quick move of "count" packets from input/output queues.
     *  POLL_AND_CHECK_STATUS: as above, plus check status registers or do
     *      other more expensive operations. This command is issued periodically
     *      but less frequently than POLL_ONLY.
     *
     * The count limit specifies how much work the handler can do during the
     * call -- typically this is the number of packets to be received, or
     * transmitted, etc. (drivers are free to interpret this number, as long
     * as the max time spent in the function grows roughly linearly with the
     * count).
     *
     * Polling is enabled and disabled via setting IFCAP_POLLING flag on
     * the interface. The driver ioctl handler should register interface
     * with polling and disable interrupts, if registration was successful.
     *
     * A second variable controls the sharing of CPU between polling/kernel
     * network processing, and other activities (typically userlevel tasks):
     * kern.polling.user_frac (between 0 and 100, default 50) sets the share
     * of CPU allocated to user tasks. CPU is allocated proportionally to the
     * shares, by dynamically adjusting the "count" (poll_burst).
     *
     * Other parameters can should be left to their default values.
     * The following constraints hold
     *
     *      1 <= poll_each_burst <= poll_burst <= poll_burst_max
     *      MIN_POLL_BURST_MAX <= poll_burst_max <= MAX_POLL_BURST_MAX
     */
    
    #define MIN_POLL_BURST_MAX      10
    #define MAX_POLL_BURST_MAX      20000
    
    static uint32_t poll_burst = 5;
   static uint32_t poll_burst_max = 150;   /* good for 100Mbit net and HZ=1000 */
   static uint32_t poll_each_burst = 5;
   
   static SYSCTL_NODE(_kern, OID_AUTO, polling, CTLFLAG_RW, 0,
           "Device polling parameters");
   
   SYSCTL_UINT(_kern_polling, OID_AUTO, burst, CTLFLAG_RD,
           &poll_burst, 0, "Current polling burst size");
   
   static int      netisr_poll_scheduled;
   static int      netisr_pollmore_scheduled;
   static int      poll_shutting_down;
   
   static int poll_burst_max_sysctl(SYSCTL_HANDLER_ARGS)
   {
           uint32_t val = poll_burst_max;
           int error;
   
           error = sysctl_handle_int(oidp, &val, 0, req);
           if (error || !req->newptr )
                   return (error);
           if (val < MIN_POLL_BURST_MAX || val > MAX_POLL_BURST_MAX)
                   return (EINVAL);
   
           mtx_lock(&poll_mtx);
           poll_burst_max = val;
           if (poll_burst > poll_burst_max)
                   poll_burst = poll_burst_max;
           if (poll_each_burst > poll_burst_max)
                   poll_each_burst = MIN_POLL_BURST_MAX;
           mtx_unlock(&poll_mtx);
   
           return (0);
   }
   SYSCTL_PROC(_kern_polling, OID_AUTO, burst_max, CTLTYPE_UINT | CTLFLAG_RW,
           0, sizeof(uint32_t), poll_burst_max_sysctl, "I", "Max Polling burst size");
   
   static int poll_each_burst_sysctl(SYSCTL_HANDLER_ARGS)
   {
           uint32_t val = poll_each_burst;
           int error;
   
           error = sysctl_handle_int(oidp, &val, 0, req);
           if (error || !req->newptr )
                   return (error);
           if (val < 1)
                   return (EINVAL);
   
           mtx_lock(&poll_mtx);
           if (val > poll_burst_max) {
                   mtx_unlock(&poll_mtx);
                   return (EINVAL);
           }
           poll_each_burst = val;
           mtx_unlock(&poll_mtx);
   
           return (0);
   }
   SYSCTL_PROC(_kern_polling, OID_AUTO, each_burst, CTLTYPE_UINT | CTLFLAG_RW,
           0, sizeof(uint32_t), poll_each_burst_sysctl, "I",
           "Max size of each burst");
   
   static uint32_t poll_in_idle_loop=0;    /* do we poll in idle loop ? */
   SYSCTL_UINT(_kern_polling, OID_AUTO, idle_poll, CTLFLAG_RW,
           &poll_in_idle_loop, 0, "Enable device polling in idle loop");
   
   static uint32_t user_frac = 50;
   static int user_frac_sysctl(SYSCTL_HANDLER_ARGS)
   {
           uint32_t val = user_frac;
           int error;
   
           error = sysctl_handle_int(oidp, &val, 0, req);
           if (error || !req->newptr )
                   return (error);
           if (val > 99)
                   return (EINVAL);
   
           mtx_lock(&poll_mtx);
           user_frac = val;
           mtx_unlock(&poll_mtx);
   
           return (0);
   }
   SYSCTL_PROC(_kern_polling, OID_AUTO, user_frac, CTLTYPE_UINT | CTLFLAG_RW,
           0, sizeof(uint32_t), user_frac_sysctl, "I",
           "Desired user fraction of cpu time");
   
   static uint32_t reg_frac_count = 0;
   static uint32_t reg_frac = 20 ;
   static int reg_frac_sysctl(SYSCTL_HANDLER_ARGS)
   {
           uint32_t val = reg_frac;
           int error;
   
           error = sysctl_handle_int(oidp, &val, 0, req);
           if (error || !req->newptr )
                   return (error);
           if (val < 1 || val > hz)
                   return (EINVAL);
   
           mtx_lock(&poll_mtx);
           reg_frac = val;
           if (reg_frac_count >= reg_frac)
                   reg_frac_count = 0;
           mtx_unlock(&poll_mtx);
   
           return (0);
   }
   SYSCTL_PROC(_kern_polling, OID_AUTO, reg_frac, CTLTYPE_UINT | CTLFLAG_RW,
           0, sizeof(uint32_t), reg_frac_sysctl, "I",
           "Every this many cycles check registers");
   
   static uint32_t short_ticks;
   SYSCTL_UINT(_kern_polling, OID_AUTO, short_ticks, CTLFLAG_RD,
           &short_ticks, 0, "Hardclock ticks shorter than they should be");
   
   static uint32_t lost_polls;
   SYSCTL_UINT(_kern_polling, OID_AUTO, lost_polls, CTLFLAG_RD,
           &lost_polls, 0, "How many times we would have lost a poll tick");
   
   static uint32_t pending_polls;
   SYSCTL_UINT(_kern_polling, OID_AUTO, pending_polls, CTLFLAG_RD,
           &pending_polls, 0, "Do we need to poll again");
   
   static int residual_burst = 0;
   SYSCTL_INT(_kern_polling, OID_AUTO, residual_burst, CTLFLAG_RD,
           &residual_burst, 0, "# of residual cycles in burst");
   
   static uint32_t poll_handlers; /* next free entry in pr[]. */
   SYSCTL_UINT(_kern_polling, OID_AUTO, handlers, CTLFLAG_RD,
           &poll_handlers, 0, "Number of registered poll handlers");
   
   static uint32_t phase;
   SYSCTL_UINT(_kern_polling, OID_AUTO, phase, CTLFLAG_RD,
           &phase, 0, "Polling phase");
   
   static uint32_t suspect;
   SYSCTL_UINT(_kern_polling, OID_AUTO, suspect, CTLFLAG_RD,
           &suspect, 0, "suspect event");
   
   static uint32_t stalled;
   SYSCTL_UINT(_kern_polling, OID_AUTO, stalled, CTLFLAG_RD,
           &stalled, 0, "potential stalls");
   
   static uint32_t idlepoll_sleeping; /* idlepoll is sleeping */
   SYSCTL_UINT(_kern_polling, OID_AUTO, idlepoll_sleeping, CTLFLAG_RD,
           &idlepoll_sleeping, 0, "idlepoll is sleeping");
   
   
   #define POLL_LIST_LEN  128
   struct pollrec {
           poll_handler_t  *handler;
           struct ifnet    *ifp;
   };
   
   static struct pollrec pr[POLL_LIST_LEN];
   
   static void
   poll_shutdown(void *arg, int howto)
   {
   
           poll_shutting_down = 1;
   }
   
   static void
   init_device_poll(void)
   {
   
           mtx_init(&poll_mtx, "polling", NULL, MTX_DEF);
           EVENTHANDLER_REGISTER(shutdown_post_sync, poll_shutdown, NULL,
               SHUTDOWN_PRI_LAST);
   }
   SYSINIT(device_poll, SI_SUB_SOFTINTR, SI_ORDER_MIDDLE, init_device_poll, NULL);
   
   
   /*
    * Hook from hardclock. Tries to schedule a netisr, but keeps track
    * of lost ticks due to the previous handler taking too long.
    * Normally, this should not happen, because polling handler should
    * run for a short time. However, in some cases (e.g. when there are
    * changes in link status etc.) the drivers take a very long time
    * (even in the order of milliseconds) to reset and reconfigure the
    * device, causing apparent lost polls.
    *
    * The first part of the code is just for debugging purposes, and tries
    * to count how often hardclock ticks are shorter than they should,
    * meaning either stray interrupts or delayed events.
    */
   void
   hardclock_device_poll(void)
   {
           static struct timeval prev_t, t;
           int delta;
   
           if (poll_handlers == 0 || poll_shutting_down)
                   return;
   
           microuptime(&t);
           delta = (t.tv_usec - prev_t.tv_usec) +
                   (t.tv_sec - prev_t.tv_sec)*1000000;
           if (delta * hz < 500000)
                   short_ticks++;
           else
                   prev_t = t;
   
           if (pending_polls > 100) {
                   /*
                    * Too much, assume it has stalled (not always true
                    * see comment above).
                    */
                   stalled++;
                   pending_polls = 0;
                   phase = 0;
           }
   
           if (phase <= 2) {
                   if (phase != 0)
                           suspect++;
                   phase = 1;
                   netisr_poll_scheduled = 1;
                   netisr_pollmore_scheduled = 1;
                   netisr_sched_poll();
                   phase = 2;
           }
           if (pending_polls++ > 0)
                   lost_polls++;
   }
   
   /*
    * ether_poll is called from the idle loop.
    */
   static void
   ether_poll(int count)
   {
           int i;
   
           mtx_lock(&poll_mtx);
   
           if (count > poll_each_burst)
                   count = poll_each_burst;
   
           for (i = 0 ; i < poll_handlers ; i++)
                   pr[i].handler(pr[i].ifp, POLL_ONLY, count);
   
           mtx_unlock(&poll_mtx);
   }
   
   /*
    * netisr_pollmore is called after other netisr's, possibly scheduling
    * another NETISR_POLL call, or adapting the burst size for the next cycle.
    *
    * It is very bad to fetch large bursts of packets from a single card at once,
    * because the burst could take a long time to be completely processed, or
    * could saturate the intermediate queue (ipintrq or similar) leading to
    * losses or unfairness. To reduce the problem, and also to account better for
    * time spent in network-related processing, we split the burst in smaller
    * chunks of fixed size, giving control to the other netisr's between chunks.
    * This helps in improving the fairness, reducing livelock (because we
    * emulate more closely the "process to completion" that we have with
    * fastforwarding) and accounting for the work performed in low level
    * handling and forwarding.
    */
   
   static struct timeval poll_start_t;
   
   void
   netisr_pollmore(void)
   {
           struct timeval t;
           int kern_load;
   
           if (poll_handlers == 0)
                   return;
   
           mtx_lock(&poll_mtx);
           if (!netisr_pollmore_scheduled) {
                   mtx_unlock(&poll_mtx);
                   return;
           }
           netisr_pollmore_scheduled = 0;
           phase = 5;
           if (residual_burst > 0) {
                   netisr_poll_scheduled = 1;
                   netisr_pollmore_scheduled = 1;
                   netisr_sched_poll();
                   mtx_unlock(&poll_mtx);
                   /* will run immediately on return, followed by netisrs */
                   return;
           }
           /* here we can account time spent in netisr's in this tick */
           microuptime(&t);
           kern_load = (t.tv_usec - poll_start_t.tv_usec) +
                   (t.tv_sec - poll_start_t.tv_sec)*1000000;       /* us */
           kern_load = (kern_load * hz) / 10000;                   /* 0..100 */
           if (kern_load > (100 - user_frac)) { /* try decrease ticks */
                   if (poll_burst > 1)
                           poll_burst--;
           } else {
                   if (poll_burst < poll_burst_max)
                           poll_burst++;
           }
   
           pending_polls--;
           if (pending_polls == 0) /* we are done */
                   phase = 0;
           else {
                   /*
                    * Last cycle was long and caused us to miss one or more
                    * hardclock ticks. Restart processing again, but slightly
                    * reduce the burst size to prevent that this happens again.
                    */
                   poll_burst -= (poll_burst / 8);
                   if (poll_burst < 1)
                           poll_burst = 1;
                   netisr_poll_scheduled = 1;
                   netisr_pollmore_scheduled = 1;
                   netisr_sched_poll();
                   phase = 6;
           }
           mtx_unlock(&poll_mtx);
   }
   
   /*
    * netisr_poll is typically scheduled once per tick.
    */
   void
   netisr_poll(void)
   {
           int i, cycles;
           enum poll_cmd arg = POLL_ONLY;
   
           if (poll_handlers == 0)
                   return;
   
           mtx_lock(&poll_mtx);
           if (!netisr_poll_scheduled) {
                   mtx_unlock(&poll_mtx);
                   return;
           }
           netisr_poll_scheduled = 0;
           phase = 3;
           if (residual_burst == 0) { /* first call in this tick */
                   microuptime(&poll_start_t);
                   if (++reg_frac_count == reg_frac) {
                           arg = POLL_AND_CHECK_STATUS;
                           reg_frac_count = 0;
                   }
   
                   residual_burst = poll_burst;
           }
           cycles = (residual_burst < poll_each_burst) ?
                   residual_burst : poll_each_burst;
           residual_burst -= cycles;
   
           for (i = 0 ; i < poll_handlers ; i++)
                   pr[i].handler(pr[i].ifp, arg, cycles);
   
           phase = 4;
           mtx_unlock(&poll_mtx);
   }
   
   /*
    * Try to register routine for polling. Returns 0 if successful
    * (and polling should be enabled), error code otherwise.
    * A device is not supposed to register itself multiple times.
    *
    * This is called from within the *_ioctl() functions.
    */
   int
   ether_poll_register(poll_handler_t *h, if_t ifp)
   {
           int i;
   
           KASSERT(h != NULL, ("%s: handler is NULL", __func__));
           KASSERT(ifp != NULL, ("%s: ifp is NULL", __func__));
   
           mtx_lock(&poll_mtx);
           if (poll_handlers >= POLL_LIST_LEN) {
                   /*
                    * List full, cannot register more entries.
                    * This should never happen; if it does, it is probably a
                    * broken driver trying to register multiple times. Checking
                    * this at runtime is expensive, and won't solve the problem
                    * anyways, so just report a few times and then give up.
                    */
                   static int verbose = 10 ;
                   if (verbose >0) {
                           log(LOG_ERR, "poll handlers list full, "
                               "maybe a broken driver ?\n");
                           verbose--;
                   }
                   mtx_unlock(&poll_mtx);
                   return (ENOMEM); /* no polling for you */
           }
   
           for (i = 0 ; i < poll_handlers ; i++)
                   if (pr[i].ifp == ifp && pr[i].handler != NULL) {
                           mtx_unlock(&poll_mtx);
                           log(LOG_DEBUG, "ether_poll_register: %s: handler"
                               " already registered\n", ifp->if_xname);
                           return (EEXIST);
                   }
   
           pr[poll_handlers].handler = h;
           pr[poll_handlers].ifp = ifp;
           poll_handlers++;
           mtx_unlock(&poll_mtx);
           if (idlepoll_sleeping)
                   wakeup(&idlepoll_sleeping);
           return (0);
   }
   
   /*
    * Remove interface from the polling list. Called from *_ioctl(), too.
    */
   int
   ether_poll_deregister(if_t ifp)
   {
           int i;
   
           KASSERT(ifp != NULL, ("%s: ifp is NULL", __func__));
   
           mtx_lock(&poll_mtx);
   
           for (i = 0 ; i < poll_handlers ; i++)
                   if (pr[i].ifp == ifp) /* found it */
                           break;
           if (i == poll_handlers) {
                   log(LOG_DEBUG, "ether_poll_deregister: %s: not found!\n",
                       ifp->if_xname);
                   mtx_unlock(&poll_mtx);
                   return (ENOENT);
           }
           poll_handlers--;
           if (i < poll_handlers) { /* Last entry replaces this one. */
                   pr[i].handler = pr[poll_handlers].handler;
                   pr[i].ifp = pr[poll_handlers].ifp;
           }
           mtx_unlock(&poll_mtx);
           return (0);
   }
   
   static void
   poll_idle(void)
   {
           struct thread *td = curthread;
           struct rtprio rtp;
   
           rtp.prio = RTP_PRIO_MAX;        /* lowest priority */
           rtp.type = RTP_PRIO_IDLE;
           PROC_SLOCK(td->td_proc);
           rtp_to_pri(&rtp, td);
           PROC_SUNLOCK(td->td_proc);
   
           for (;;) {
                   if (poll_in_idle_loop && poll_handlers > 0) {
                           idlepoll_sleeping = 0;
                           ether_poll(poll_each_burst);
                           thread_lock(td);
                           mi_switch(SW_VOL, NULL);
                           thread_unlock(td);
                   } else {
                           idlepoll_sleeping = 1;
                           tsleep(&idlepoll_sleeping, 0, "pollid", hz * 3);
                   }
           }
   }
   
   static struct proc *idlepoll;
   static struct kproc_desc idlepoll_kp = {
            "idlepoll",
            poll_idle,
            &idlepoll
   };
   SYSINIT(idlepoll, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, kproc_start,
       &idlepoll_kp);

Cache object: a6ae5590a3d80034c983e40b6ebe5e5e