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

     /*-
      * 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.
     *
     * $FreeBSD$
     */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/socket.h>                 /* needed by net/if.h           */
    #include <sys/sysctl.h>
    
    #include <i386/include/md_var.h>        /* for vm_page_zero_idle()      */
    #include <net/if.h>                     /* for IFF_* flags              */
    #include <net/netisr.h>                 /* for NETISR_POLL              */
    
    #ifdef SMP
    #include "opt_lint.h"
    #ifndef COMPILING_LINT
    #error DEVICE_POLLING is not compatible with SMP
    #endif
    #endif
    
    static void netisr_poll(void);          /* the two netisr handlers      */
    static void netisr_pollmore(void);
    
    void init_device_poll(void);            /* init routine                 */
    void hardclock_device_poll(void);       /* hook from hardclock          */
    void ether_poll(int);                   /* polling while in trap        */
    int idle_poll(void);                    /* poll while in idle loop      */
    
    /*
     * Polling support for [network] device drivers.
     *
     * Drivers which support this feature try to 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.
     *  POLL_DEREGISTER: deregister and return to interrupt mode.
     *
     * The first two commands are only issued if the interface is marked as
     * 'IFF_UP and IFF_RUNNING', the last one only if IFF_RUNNING is set.
     *
     * 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).
     *
     * Deregistration can be requested by the driver itself (typically in the
     * *_stop() routine), or by the polling code, by invoking the handler.
     *
     * Polling can be globally enabled or disabled with the sysctl variable
     * kern.polling.enable (default is 0, disabled)
     *
     * 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
     *      0 <= poll_in_trap <= poll_each_burst
     *      MIN_POLL_BURST_MAX <= poll_burst_max <= MAX_POLL_BURST_MAX
    */
   
   #define MIN_POLL_BURST_MAX      10
   #define MAX_POLL_BURST_MAX      1000
   
   SYSCTL_NODE(_kern, OID_AUTO, polling, CTLFLAG_RW, 0,
           "Device polling parameters");
   
   static u_int32_t poll_burst = 5;
   SYSCTL_UINT(_kern_polling, OID_AUTO, burst, CTLFLAG_RW,
           &poll_burst, 0, "Current polling burst size");
   
   static u_int32_t poll_each_burst = 5;
   SYSCTL_UINT(_kern_polling, OID_AUTO, each_burst, CTLFLAG_RW,
           &poll_each_burst, 0, "Max size of each burst");
   
   static u_int32_t poll_burst_max = 150;  /* good for 100Mbit net and HZ=1000 */
   SYSCTL_UINT(_kern_polling, OID_AUTO, burst_max, CTLFLAG_RW,
           &poll_burst_max, 0, "Max Polling burst size");
   
   static u_int32_t poll_in_idle_loop=1;           /* 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");
   
   u_int32_t poll_in_trap;                 /* used in trap.c */
   SYSCTL_UINT(_kern_polling, OID_AUTO, poll_in_trap, CTLFLAG_RW,
           &poll_in_trap, 0, "Poll burst size during a trap");
   
   static u_int32_t user_frac = 50;
   SYSCTL_UINT(_kern_polling, OID_AUTO, user_frac, CTLFLAG_RW,
           &user_frac, 0, "Desired user fraction of cpu time");
   
   static u_int32_t reg_frac = 20 ;
   SYSCTL_UINT(_kern_polling, OID_AUTO, reg_frac, CTLFLAG_RW,
           &reg_frac, 0, "Every this many cycles poll register");
   
   static u_int32_t short_ticks;
   SYSCTL_UINT(_kern_polling, OID_AUTO, short_ticks, CTLFLAG_RW,
           &short_ticks, 0, "Hardclock ticks shorter than they should be");
   
   static u_int32_t lost_polls;
   SYSCTL_UINT(_kern_polling, OID_AUTO, lost_polls, CTLFLAG_RW,
           &lost_polls, 0, "How many times we would have lost a poll tick");
   
   static u_int32_t pending_polls;
   SYSCTL_UINT(_kern_polling, OID_AUTO, pending_polls, CTLFLAG_RW,
           &pending_polls, 0, "Do we need to poll again");
   
   static int residual_burst = 0;
   SYSCTL_INT(_kern_polling, OID_AUTO, residual_burst, CTLFLAG_RW,
           &residual_burst, 0, "# of residual cycles in burst");
   
   static u_int32_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 int polling = 0;         /* global polling enable */
   SYSCTL_UINT(_kern_polling, OID_AUTO, enable, CTLFLAG_RW,
           &polling, 0, "Polling enabled");
   
   static u_int32_t phase;
   SYSCTL_UINT(_kern_polling, OID_AUTO, phase, CTLFLAG_RW,
           &phase, 0, "Polling phase");
   
   static u_int32_t suspect;
   SYSCTL_UINT(_kern_polling, OID_AUTO, suspect, CTLFLAG_RW,
           &suspect, 0, "suspect event");
   
   static u_int32_t stalled;
   SYSCTL_UINT(_kern_polling, OID_AUTO, stalled, CTLFLAG_RW,
           &stalled, 0, "potential stalls");
   
   
   #define POLL_LIST_LEN  128
   struct pollrec {
           poll_handler_t  *handler;
           struct ifnet    *ifp;
   };
   
   static struct pollrec pr[POLL_LIST_LEN];
   
   /*
    * register relevant netisr. Called from kern_clock.c:
    */
   void
   init_device_poll(void)
   {
           register_netisr(NETISR_POLL, netisr_poll);
           register_netisr(NETISR_POLLMORE, netisr_pollmore);
   }
   
   /*
    * 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)
                   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;
                   schednetisr(NETISR_POLL);
                   phase = 2;
           }
           if (pending_polls++ > 0)
                   lost_polls++;
   }
   
   /*
    * ether_poll is called from the idle loop or from the trap handler.
    */
   void
   ether_poll(int count)
   {
           int i;
           int s = splimp();
   
           if (count > poll_each_burst)
                   count = poll_each_burst;
           for (i = 0 ; i < poll_handlers ; i++)
                   if (pr[i].handler && (IFF_UP|IFF_RUNNING) ==
                       (pr[i].ifp->if_flags & (IFF_UP|IFF_RUNNING)) )
                           pr[i].handler(pr[i].ifp, 0, count); /* quick check */
           splx(s);
   }
   
   /*
    * idle_poll is replaces the body of the idle loop when DEVICE_POLLING
    * is used.
    */
   int
   idle_poll(void)
   {
           if (poll_in_idle_loop && poll_handlers > 0) {
                   int s = splimp();
                   enable_intr();
                   ether_poll(poll_each_burst);
                   disable_intr();
                   splx(s);
                   vm_page_zero_idle();
                   return 1;
           } else
                   return vm_page_zero_idle();
   }
   
   /*
    * 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;
   
   static void
   netisr_pollmore()
   {
           struct timeval t;
           int kern_load;
           int s = splhigh();
   
           phase = 5;
           if (residual_burst > 0) {
                   schednetisr(NETISR_POLL);
                   /* will run immediately on return, followed by netisrs */
                   splx(s);
                   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;
                   schednetisr(NETISR_POLL);
                   phase = 6;
           }
           splx(s);
   }
   
   /*
    * netisr_poll is scheduled by schednetisr when appropriate, typically once
    * per tick. It is called at splnet() so first thing to do is to upgrade to
    * splimp(), and call all registered handlers.
    */
   static void
   netisr_poll(void)
   {
           static int reg_frac_count;
           int i, cycles;
           enum poll_cmd arg = POLL_ONLY;
           int s=splimp();
   
           phase = 3;
           if (residual_burst == 0) { /* first call in this tick */
                   microuptime(&poll_start_t);
                   /*
                    * Check that paremeters are consistent with runtime
                    * variables. Some of these tests could be done at sysctl
                    * time, but the savings would be very limited because we
                    * still have to check against reg_frac_count and
                    * poll_each_burst. So, instead of writing separate sysctl
                    * handlers, we do all here.
                    */
   
                   if (reg_frac > hz)
                           reg_frac = hz;
                   else if (reg_frac < 1)
                           reg_frac = 1;
                   if (reg_frac_count > reg_frac)
                           reg_frac_count = reg_frac - 1;
                   if (reg_frac_count-- == 0) {
                           arg = POLL_AND_CHECK_STATUS;
                           reg_frac_count = reg_frac - 1;
                   }
                   if (poll_burst_max < MIN_POLL_BURST_MAX)
                           poll_burst_max = MIN_POLL_BURST_MAX;
                   else if (poll_burst_max > MAX_POLL_BURST_MAX)
                           poll_burst_max = MAX_POLL_BURST_MAX;
   
                   if (poll_each_burst < 1)
                           poll_each_burst = 1;
                   else if (poll_each_burst > poll_burst_max)
                           poll_each_burst = poll_burst_max;
   
                   if (poll_burst > poll_burst_max)
                           poll_burst = poll_burst_max;
                   residual_burst = poll_burst;
           }
           cycles = (residual_burst < poll_each_burst) ?
                   residual_burst : poll_each_burst;
           residual_burst -= cycles;
   
           if (polling) {
                   for (i = 0 ; i < poll_handlers ; i++)
                           if (pr[i].handler && (IFF_UP|IFF_RUNNING) ==
                               (pr[i].ifp->if_flags & (IFF_UP|IFF_RUNNING)) )
                                   pr[i].handler(pr[i].ifp, arg, cycles);
           } else {        /* unregister */
                   for (i = 0 ; i < poll_handlers ; i++) {
                           if (pr[i].handler &&
                               pr[i].ifp->if_flags & IFF_RUNNING) {
                                   pr[i].ifp->if_ipending &= ~IFF_POLLING;
                                   pr[i].handler(pr[i].ifp, POLL_DEREGISTER, 1);
                           }
                           pr[i].handler=NULL;
                   }
                   residual_burst = 0;
                   poll_handlers = 0;
           }
           schednetisr(NETISR_POLLMORE);
           phase = 4;
           splx(s);
   }
   
   /*
    * Try to register routine for polling. Returns 1 if successful
    * (and polling should be enabled), 0 otherwise.
    * A device is not supposed to register itself multiple times.
    *
    * This is called from within the *_intr() functions, so we do not need
    * further locking.
    */
   int
   ether_poll_register(poll_handler_t *h, struct ifnet *ifp)
   {
           int s;
   
           if (polling == 0) /* polling disabled, cannot register */
                   return 0;
           if (h == NULL || ifp == NULL)           /* bad arguments        */
                   return 0;
           if ( !(ifp->if_flags & IFF_UP) )        /* must be up           */
                   return 0;
           if (ifp->if_ipending & IFF_POLLING)     /* already polling      */
                   return 0;
   
           s = splhigh();
           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 ;
                   splx(s);
                   if (verbose >0) {
                           printf("poll handlers list full, "
                                   "maybe a broken driver ?\n");
                           verbose--;
                   }
                   return 0; /* no polling for you */
           }
   
           pr[poll_handlers].handler = h;
           pr[poll_handlers].ifp = ifp;
           poll_handlers++;
           ifp->if_ipending |= IFF_POLLING;
           splx(s);
           return 1; /* polling enabled in next call */
   }
   
   /*
    * Remove interface from the polling list. Normally called by *_stop().
    * It is not an error to call it with IFF_POLLING clear, the call is
    * sufficiently rare to be preferable to save the space for the extra
    * test in each driver in exchange of one additional function call.
    */
   int
   ether_poll_deregister(struct ifnet *ifp)
   {
           int i;
           int s = splimp();
           
           if ( !ifp || !(ifp->if_ipending & IFF_POLLING) ) {
                   splx(s);
                   return 0;
           }
           for (i = 0 ; i < poll_handlers ; i++)
                   if (pr[i].ifp == ifp) /* found it */
                           break;
           ifp->if_ipending &= ~IFF_POLLING; /* found or not... */
           if (i == poll_handlers) {
                   splx(s);
                   printf("ether_poll_deregister: ifp not found!!!\n");
                   return 0;
           }
           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;
           }
           splx(s);
           return 1;
   }

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