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

     /*
      * Copyright (c) 2003,2004 The DragonFly Project.  All rights reserved.
      * 
      * This code is derived from software contributed to The DragonFly Project
      * by Matthew Dillon <dillon@backplane.com>
      * 
      * 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.
     * 3. Neither the name of The DragonFly Project nor the names of its
     *    contributors may be used to endorse or promote products derived
     *    from this software without specific, prior written permission.
     * 
     * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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
     * COPYRIGHT HOLDERS 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.
     */
    
    /*
     * This module implements IPI message queueing and the MI portion of IPI
     * message processing.
     */
    
    #include "opt_ddb.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/proc.h>
    #include <sys/rtprio.h>
    #include <sys/queue.h>
    #include <sys/thread2.h>
    #include <sys/sysctl.h>
    #include <sys/ktr.h>
    #include <sys/kthread.h>
    #include <machine/cpu.h>
    #include <sys/lock.h>
    
    #include <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/vm_kern.h>
    #include <vm/vm_object.h>
    #include <vm/vm_page.h>
    #include <vm/vm_map.h>
    #include <vm/vm_pager.h>
    #include <vm/vm_extern.h>
    #include <vm/vm_zone.h>
    
    #include <machine/stdarg.h>
    #include <machine/smp.h>
    #include <machine/atomic.h>
    
    #ifdef _KERNEL_VIRTUAL
    #include <pthread.h>
    #endif
    
    struct ipiq_stats {
        __int64_t ipiq_count;       /* total calls to lwkt_send_ipiq*() */
        __int64_t ipiq_fifofull;    /* number of fifo full conditions detected */
        __int64_t ipiq_avoided;     /* interlock with target avoids cpu ipi */
        __int64_t ipiq_passive;     /* passive IPI messages */
        __int64_t ipiq_cscount;     /* number of cpu synchronizations */
    } __cachealign;
    
    static struct ipiq_stats ipiq_stats_percpu[MAXCPU];
    #define ipiq_stat(gd)   ipiq_stats_percpu[(gd)->gd_cpuid]
    
    static int ipiq_debug;          /* set to 1 for debug */
    #ifdef PANIC_DEBUG
    static int      panic_ipiq_cpu = -1;
    static int      panic_ipiq_count = 100;
    #endif
    
    SYSCTL_INT(_lwkt, OID_AUTO, ipiq_debug, CTLFLAG_RW, &ipiq_debug, 0,
        "");
    #ifdef PANIC_DEBUG
    SYSCTL_INT(_lwkt, OID_AUTO, panic_ipiq_cpu, CTLFLAG_RW, &panic_ipiq_cpu, 0, "");
    SYSCTL_INT(_lwkt, OID_AUTO, panic_ipiq_count, CTLFLAG_RW, &panic_ipiq_count, 0, "");
    #endif
    
    #define IPIQ_STRING     "func=%p arg1=%p arg2=%d scpu=%d dcpu=%d"
    #define IPIQ_ARGS       void *func, void *arg1, int arg2, int scpu, int dcpu
    
   #if !defined(KTR_IPIQ)
   #define KTR_IPIQ        KTR_ALL
   #endif
   KTR_INFO_MASTER(ipiq);
   KTR_INFO(KTR_IPIQ, ipiq, send_norm, 0, IPIQ_STRING, IPIQ_ARGS);
   KTR_INFO(KTR_IPIQ, ipiq, send_pasv, 1, IPIQ_STRING, IPIQ_ARGS);
   KTR_INFO(KTR_IPIQ, ipiq, send_nbio, 2, IPIQ_STRING, IPIQ_ARGS);
   KTR_INFO(KTR_IPIQ, ipiq, send_fail, 3, IPIQ_STRING, IPIQ_ARGS);
   KTR_INFO(KTR_IPIQ, ipiq, receive, 4, IPIQ_STRING, IPIQ_ARGS);
   KTR_INFO(KTR_IPIQ, ipiq, sync_start, 5, "cpumask=%08lx", unsigned long mask);
   KTR_INFO(KTR_IPIQ, ipiq, sync_end, 6, "cpumask=%08lx", unsigned long mask);
   KTR_INFO(KTR_IPIQ, ipiq, cpu_send, 7, IPIQ_STRING, IPIQ_ARGS);
   KTR_INFO(KTR_IPIQ, ipiq, send_end, 8, IPIQ_STRING, IPIQ_ARGS);
   
   #define logipiq(name, func, arg1, arg2, sgd, dgd)       \
           KTR_LOG(ipiq_ ## name, func, arg1, arg2, sgd->gd_cpuid, dgd->gd_cpuid)
   #define logipiq2(name, arg)     \
           KTR_LOG(ipiq_ ## name, arg)
   
   static int lwkt_process_ipiq_core(globaldata_t sgd, lwkt_ipiq_t ip, 
                                     struct intrframe *frame);
   static void lwkt_cpusync_remote1(lwkt_cpusync_t cs);
   static void lwkt_cpusync_remote2(lwkt_cpusync_t cs);
   
   #define IPIQ_SYSCTL(name) \
   static int \
   sysctl_##name(SYSCTL_HANDLER_ARGS) \
   { \
       __int64_t val = 0; \
       int cpu, error; \
    \
       for (cpu = 0; cpu < ncpus; ++cpu) \
           val += ipiq_stats_percpu[cpu].name; \
    \
       error = sysctl_handle_quad(oidp, &val, 0, req); \
       if (error || req->newptr == NULL) \
           return error; \
    \
       for (cpu = 0; cpu < ncpus; ++cpu) \
           ipiq_stats_percpu[cpu].name = val; \
    \
       return 0; \
   }
   
   IPIQ_SYSCTL(ipiq_count);
   IPIQ_SYSCTL(ipiq_fifofull);
   IPIQ_SYSCTL(ipiq_avoided);
   IPIQ_SYSCTL(ipiq_passive);
   IPIQ_SYSCTL(ipiq_cscount);
   
   SYSCTL_PROC(_lwkt, OID_AUTO, ipiq_count, (CTLTYPE_QUAD | CTLFLAG_RW),
       0, 0, sysctl_ipiq_count, "Q", "Number of IPI's sent");
   SYSCTL_PROC(_lwkt, OID_AUTO, ipiq_fifofull, (CTLTYPE_QUAD | CTLFLAG_RW),
       0, 0, sysctl_ipiq_fifofull, "Q",
       "Number of fifo full conditions detected");
   SYSCTL_PROC(_lwkt, OID_AUTO, ipiq_avoided, (CTLTYPE_QUAD | CTLFLAG_RW),
       0, 0, sysctl_ipiq_avoided, "Q",
       "Number of IPI's avoided by interlock with target cpu");
   SYSCTL_PROC(_lwkt, OID_AUTO, ipiq_passive, (CTLTYPE_QUAD | CTLFLAG_RW),
       0, 0, sysctl_ipiq_passive, "Q",
       "Number of passive IPI messages sent");
   SYSCTL_PROC(_lwkt, OID_AUTO, ipiq_cscount, (CTLTYPE_QUAD | CTLFLAG_RW),
       0, 0, sysctl_ipiq_cscount, "Q",
       "Number of cpu synchronizations");
   
   /*
    * Send a function execution request to another cpu.  The request is queued
    * on the cpu<->cpu ipiq matrix.  Each cpu owns a unique ipiq FIFO for every
    * possible target cpu.  The FIFO can be written.
    *
    * If the FIFO fills up we have to enable interrupts to avoid an APIC
    * deadlock and process pending IPIQs while waiting for it to empty.   
    * Otherwise we may soft-deadlock with another cpu whos FIFO is also full.
    *
    * We can safely bump gd_intr_nesting_level because our crit_exit() at the
    * end will take care of any pending interrupts.
    *
    * The actual hardware IPI is avoided if the target cpu is already processing
    * the queue from a prior IPI.  It is possible to pipeline IPI messages
    * very quickly between cpus due to the FIFO hysteresis.
    *
    * Need not be called from a critical section.
    */
   int
   lwkt_send_ipiq3(globaldata_t target, ipifunc3_t func, void *arg1, int arg2)
   {
       lwkt_ipiq_t ip;
       int windex;
   #ifdef _KERNEL_VIRTUAL
       int repeating = 0;
   #endif
       struct globaldata *gd = mycpu;
   
       logipiq(send_norm, func, arg1, arg2, gd, target);
   
       if (target == gd) {
           func(arg1, arg2, NULL);
           logipiq(send_end, func, arg1, arg2, gd, target);
           return(0);
       } 
       crit_enter();
       ++gd->gd_intr_nesting_level;
   #ifdef INVARIANTS
       if (gd->gd_intr_nesting_level > 20)
           panic("lwkt_send_ipiq: TOO HEAVILY NESTED!");
   #endif
       KKASSERT(curthread->td_critcount);
       ++ipiq_stat(gd).ipiq_count;
       ip = &gd->gd_ipiq[target->gd_cpuid];
   
       /*
        * Do not allow the FIFO to become full.  Interrupts must be physically
        * enabled while we liveloop to avoid deadlocking the APIC.
        *
        * The target ipiq may have gotten filled up due to passive IPIs and thus
        * not be aware that its queue is too full, so be sure to issue an
        * ipiq interrupt to the target cpu.
        */
       if (ip->ip_windex - ip->ip_rindex > MAXCPUFIFO / 2) {
   #if defined(__i386__)
           unsigned int eflags = read_eflags();
   #elif defined(__x86_64__)
           unsigned long rflags = read_rflags();
   #endif
   
           cpu_enable_intr();
           ++ipiq_stat(gd).ipiq_fifofull;
           DEBUG_PUSH_INFO("send_ipiq3");
           while (ip->ip_windex - ip->ip_rindex > MAXCPUFIFO / 4) {
               if (atomic_poll_acquire_int(&target->gd_npoll)) {
                   logipiq(cpu_send, func, arg1, arg2, gd, target);
                   cpu_send_ipiq(target->gd_cpuid);
               }
               KKASSERT(ip->ip_windex - ip->ip_rindex != MAXCPUFIFO - 1);
               lwkt_process_ipiq();
               cpu_pause();
   #ifdef _KERNEL_VIRTUAL
               if (repeating++ > 10)
                       pthread_yield();
   #endif
           }
           DEBUG_POP_INFO();
   #if defined(__i386__)
           write_eflags(eflags);
   #elif defined(__x86_64__)
           write_rflags(rflags);
   #endif
       }
   
       /*
        * Queue the new message
        */
       windex = ip->ip_windex & MAXCPUFIFO_MASK;
       ip->ip_info[windex].func = func;
       ip->ip_info[windex].arg1 = arg1;
       ip->ip_info[windex].arg2 = arg2;
       cpu_sfence();
       ++ip->ip_windex;
       atomic_set_cpumask(&target->gd_ipimask, gd->gd_cpumask);
   
       /*
        * signal the target cpu that there is work pending.
        */
       if (atomic_poll_acquire_int(&target->gd_npoll)) {
           logipiq(cpu_send, func, arg1, arg2, gd, target);
           cpu_send_ipiq(target->gd_cpuid);
       } else {
           ++ipiq_stat(gd).ipiq_avoided;
       }
       --gd->gd_intr_nesting_level;
       crit_exit();
       logipiq(send_end, func, arg1, arg2, gd, target);
   
       return(ip->ip_windex);
   }
   
   /*
    * Similar to lwkt_send_ipiq() but this function does not actually initiate
    * the IPI to the target cpu unless the FIFO has become too full, so it is
    * very fast.
    *
    * This function is used for non-critical IPI messages, such as memory
    * deallocations.  The queue will typically be flushed by the target cpu at
    * the next clock interrupt.
    *
    * Need not be called from a critical section.
    */
   int
   lwkt_send_ipiq3_passive(globaldata_t target, ipifunc3_t func,
                           void *arg1, int arg2)
   {
       lwkt_ipiq_t ip;
       int windex;
   #ifdef _KERNEL_VIRTUAL
       int repeating = 0;
   #endif
       struct globaldata *gd = mycpu;
   
       KKASSERT(target != gd);
       crit_enter();
       ++gd->gd_intr_nesting_level;
       logipiq(send_pasv, func, arg1, arg2, gd, target);
   #ifdef INVARIANTS
       if (gd->gd_intr_nesting_level > 20)
           panic("lwkt_send_ipiq: TOO HEAVILY NESTED!");
   #endif
       KKASSERT(curthread->td_critcount);
       ++ipiq_stat(gd).ipiq_count;
       ++ipiq_stat(gd).ipiq_passive;
       ip = &gd->gd_ipiq[target->gd_cpuid];
   
       /*
        * Do not allow the FIFO to become full.  Interrupts must be physically
        * enabled while we liveloop to avoid deadlocking the APIC.
        */
       if (ip->ip_windex - ip->ip_rindex > MAXCPUFIFO / 2) {
   #if defined(__i386__)
           unsigned int eflags = read_eflags();
   #elif defined(__x86_64__)
           unsigned long rflags = read_rflags();
   #endif
   
           cpu_enable_intr();
           ++ipiq_stat(gd).ipiq_fifofull;
           DEBUG_PUSH_INFO("send_ipiq3_passive");
           while (ip->ip_windex - ip->ip_rindex > MAXCPUFIFO / 4) {
               if (atomic_poll_acquire_int(&target->gd_npoll)) {
                   logipiq(cpu_send, func, arg1, arg2, gd, target);
                   cpu_send_ipiq(target->gd_cpuid);
               }
               KKASSERT(ip->ip_windex - ip->ip_rindex != MAXCPUFIFO - 1);
               lwkt_process_ipiq();
               cpu_pause();
   #ifdef _KERNEL_VIRTUAL
               if (repeating++ > 10)
                       pthread_yield();
   #endif
           }
           DEBUG_POP_INFO();
   #if defined(__i386__)
           write_eflags(eflags);
   #elif defined(__x86_64__)
           write_rflags(rflags);
   #endif
       }
   
       /*
        * Queue the new message
        */
       windex = ip->ip_windex & MAXCPUFIFO_MASK;
       ip->ip_info[windex].func = func;
       ip->ip_info[windex].arg1 = arg1;
       ip->ip_info[windex].arg2 = arg2;
       cpu_sfence();
       ++ip->ip_windex;
       atomic_set_cpumask(&target->gd_ipimask, gd->gd_cpumask);
       --gd->gd_intr_nesting_level;
   
       /*
        * Do not signal the target cpu, it will pick up the IPI when it next
        * polls (typically on the next tick).
        */
       crit_exit();
       logipiq(send_end, func, arg1, arg2, gd, target);
   
       return(ip->ip_windex);
   }
   
   /*
    * Send an IPI request without blocking, return 0 on success, ENOENT on 
    * failure.  The actual queueing of the hardware IPI may still force us
    * to spin and process incoming IPIs but that will eventually go away
    * when we've gotten rid of the other general IPIs.
    */
   int
   lwkt_send_ipiq3_nowait(globaldata_t target, ipifunc3_t func, 
                          void *arg1, int arg2)
   {
       lwkt_ipiq_t ip;
       int windex;
       struct globaldata *gd = mycpu;
   
       logipiq(send_nbio, func, arg1, arg2, gd, target);
       KKASSERT(curthread->td_critcount);
       if (target == gd) {
           func(arg1, arg2, NULL);
           logipiq(send_end, func, arg1, arg2, gd, target);
           return(0);
       } 
       crit_enter();
       ++gd->gd_intr_nesting_level;
       ++ipiq_stat(gd).ipiq_count;
       ip = &gd->gd_ipiq[target->gd_cpuid];
   
       if (ip->ip_windex - ip->ip_rindex >= MAXCPUFIFO * 2 / 3) {
           logipiq(send_fail, func, arg1, arg2, gd, target);
           --gd->gd_intr_nesting_level;
           crit_exit();
           return(ENOENT);
       }
       windex = ip->ip_windex & MAXCPUFIFO_MASK;
       ip->ip_info[windex].func = func;
       ip->ip_info[windex].arg1 = arg1;
       ip->ip_info[windex].arg2 = arg2;
       cpu_sfence();
       ++ip->ip_windex;
       atomic_set_cpumask(&target->gd_ipimask, gd->gd_cpumask);
   
       /*
        * This isn't a passive IPI, we still have to signal the target cpu.
        */
       if (atomic_poll_acquire_int(&target->gd_npoll)) {
           logipiq(cpu_send, func, arg1, arg2, gd, target);
           cpu_send_ipiq(target->gd_cpuid);
       } else {
           ++ipiq_stat(gd).ipiq_avoided;
       }
       --gd->gd_intr_nesting_level;
       crit_exit();
   
       logipiq(send_end, func, arg1, arg2, gd, target);
       return(0);
   }
   
   /*
    * deprecated, used only by fast int forwarding.
    */
   int
   lwkt_send_ipiq3_bycpu(int dcpu, ipifunc3_t func, void *arg1, int arg2)
   {
       return(lwkt_send_ipiq3(globaldata_find(dcpu), func, arg1, arg2));
   }
   
   /*
    * Send a message to several target cpus.  Typically used for scheduling.
    * The message will not be sent to stopped cpus.
    */
   int
   lwkt_send_ipiq3_mask(cpumask_t mask, ipifunc3_t func, void *arg1, int arg2)
   {
       int cpuid;
       int count = 0;
   
       mask &= ~stopped_cpus;
       while (mask) {
           cpuid = BSFCPUMASK(mask);
           lwkt_send_ipiq3(globaldata_find(cpuid), func, arg1, arg2);
           mask &= ~CPUMASK(cpuid);
           ++count;
       }
       return(count);
   }
   
   /*
    * Wait for the remote cpu to finish processing a function.
    *
    * YYY we have to enable interrupts and process the IPIQ while waiting
    * for it to empty or we may deadlock with another cpu.  Create a CPU_*()
    * function to do this!  YYY we really should 'block' here.
    *
    * MUST be called from a critical section.  This routine may be called
    * from an interrupt (for example, if an interrupt wakes a foreign thread
    * up).
    */
   void
   lwkt_wait_ipiq(globaldata_t target, int seq)
   {
       lwkt_ipiq_t ip;
   
       if (target != mycpu) {
           ip = &mycpu->gd_ipiq[target->gd_cpuid];
           if ((int)(ip->ip_xindex - seq) < 0) {
   #if defined(__i386__)
               unsigned int eflags = read_eflags();
   #elif defined(__x86_64__)
               unsigned long rflags = read_rflags();
   #endif
               int64_t time_tgt = tsc_get_target(1000000000LL);
               int time_loops = 10;
               int benice = 0;
   #ifdef _KERNEL_VIRTUAL
               int repeating = 0;
   #endif
   
               cpu_enable_intr();
               DEBUG_PUSH_INFO("wait_ipiq");
               while ((int)(ip->ip_xindex - seq) < 0) {
                   crit_enter();
                   lwkt_process_ipiq();
                   crit_exit();
   #ifdef _KERNEL_VIRTUAL
                   if (repeating++ > 10)
                           pthread_yield();
   #endif
   
                   /*
                    * IPIQs must be handled within 10 seconds and this code
                    * will warn after one second.
                    */
                   if ((benice & 255) == 0 && tsc_test_target(time_tgt) > 0) {
                           kprintf("LWKT_WAIT_IPIQ WARNING! %d wait %d (%d)\n",
                                   mycpu->gd_cpuid, target->gd_cpuid,
                                   ip->ip_xindex - seq);
                           if (--time_loops == 0)
                                   panic("LWKT_WAIT_IPIQ");
                           time_tgt = tsc_get_target(1000000000LL);
                   }
                   ++benice;
   
                   /*
                    * xindex may be modified by another cpu, use a load fence
                    * to ensure that the loop does not use a speculative value
                    * (which may improve performance).
                    */
                   cpu_lfence();
               }
               DEBUG_POP_INFO();
   #if defined(__i386__)
               write_eflags(eflags);
   #elif defined(__x86_64__)
               write_rflags(rflags);
   #endif
           }
       }
   }
   
   int
   lwkt_seq_ipiq(globaldata_t target)
   {
       lwkt_ipiq_t ip;
   
       ip = &mycpu->gd_ipiq[target->gd_cpuid];
       return(ip->ip_windex);
   }
   
   /*
    * Called from IPI interrupt (like a fast interrupt), which has placed
    * us in a critical section.  The MP lock may or may not be held.
    * May also be called from doreti or splz, or be reentrantly called
    * indirectly through the ip_info[].func we run.
    *
    * There are two versions, one where no interrupt frame is available (when
    * called from the send code and from splz, and one where an interrupt
    * frame is available.
    *
    * When the current cpu is mastering a cpusync we do NOT internally loop
    * on the cpusyncq poll.  We also do not re-flag a pending ipi due to
    * the cpusyncq poll because this can cause doreti/splz to loop internally.
    * The cpusync master's own loop must be allowed to run to avoid a deadlock.
    */
   void
   lwkt_process_ipiq(void)
   {
       globaldata_t gd = mycpu;
       globaldata_t sgd;
       lwkt_ipiq_t ip;
       cpumask_t mask;
       int n;
   
       ++gd->gd_processing_ipiq;
   again:
       cpu_lfence();
       mask = gd->gd_ipimask;
       atomic_clear_cpumask(&gd->gd_ipimask, mask);
       while (mask) {
           n = BSFCPUMASK(mask);
           if (n != gd->gd_cpuid) {
               sgd = globaldata_find(n);
               ip = sgd->gd_ipiq;
               if (ip != NULL) {
                   while (lwkt_process_ipiq_core(sgd, &ip[gd->gd_cpuid], NULL))
                       ;
               }
           }
           mask &= ~CPUMASK(n);
       }
   
       /*
        * Process pending cpusyncs.  If the current thread has a cpusync
        * active cpusync we only run the list once and do not re-flag
        * as the thread itself is processing its interlock.
        */
       if (lwkt_process_ipiq_core(gd, &gd->gd_cpusyncq, NULL)) {
           if (gd->gd_curthread->td_cscount == 0)
               goto again;
           /* need_ipiq(); do not reflag */
       }
   
       /*
        * Interlock to allow more IPI interrupts.  Recheck ipimask after
        * releasing gd_npoll.
        */
       if (gd->gd_ipimask)
           goto again;
       atomic_poll_release_int(&gd->gd_npoll);
       cpu_mfence();
       if (gd->gd_ipimask)
           goto again;
       --gd->gd_processing_ipiq;
   }
   
   void
   lwkt_process_ipiq_frame(struct intrframe *frame)
   {
       globaldata_t gd = mycpu;
       globaldata_t sgd;
       lwkt_ipiq_t ip;
       cpumask_t mask;
       int n;
   
   again:
       cpu_lfence();
       mask = gd->gd_ipimask;
       atomic_clear_cpumask(&gd->gd_ipimask, mask);
       while (mask) {
           n = BSFCPUMASK(mask);
           if (n != gd->gd_cpuid) {
               sgd = globaldata_find(n);
               ip = sgd->gd_ipiq;
               if (ip != NULL) {
                   while (lwkt_process_ipiq_core(sgd, &ip[gd->gd_cpuid], frame))
                       ;
               }
           }
           mask &= ~CPUMASK(n);
       }
       if (gd->gd_cpusyncq.ip_rindex != gd->gd_cpusyncq.ip_windex) {
           if (lwkt_process_ipiq_core(gd, &gd->gd_cpusyncq, frame)) {
               if (gd->gd_curthread->td_cscount == 0)
                   goto again;
               /* need_ipiq(); do not reflag */
           }
       }
   
       /*
        * Interlock to allow more IPI interrupts.  Recheck ipimask after
        * releasing gd_npoll.
        */
       if (gd->gd_ipimask)
           goto again;
       atomic_poll_release_int(&gd->gd_npoll);
       cpu_mfence();
       if (gd->gd_ipimask)
           goto again;
   }
   
   #if 0
   static int iqticks[SMP_MAXCPU];
   static int iqcount[SMP_MAXCPU];
   #endif
   #if 0
   static int iqterm[SMP_MAXCPU];
   #endif
   
   static int
   lwkt_process_ipiq_core(globaldata_t sgd, lwkt_ipiq_t ip, 
                          struct intrframe *frame)
   {
       globaldata_t mygd = mycpu;
       int ri;
       int wi;
       ipifunc3_t copy_func;
       void *copy_arg1;
       int copy_arg2;
   
   #if 0
       if (iqticks[mygd->gd_cpuid] != ticks) {
               iqticks[mygd->gd_cpuid] = ticks;
               iqcount[mygd->gd_cpuid] = 0;
       }
       if (++iqcount[mygd->gd_cpuid] > 3000000) {
           kprintf("cpu %d ipiq maxed cscount %d spin %d\n",
                   mygd->gd_cpuid,
                   mygd->gd_curthread->td_cscount,
                   mygd->gd_spinlocks);
           iqcount[mygd->gd_cpuid] = 0;
   #if 0
           if (++iqterm[mygd->gd_cpuid] > 10)
                   panic("cpu %d ipiq maxed", mygd->gd_cpuid);
   #endif
           int i;
           for (i = 0; i < ncpus; ++i) {
                   if (globaldata_find(i)->gd_infomsg)
                           kprintf(" %s", globaldata_find(i)->gd_infomsg);
           }
           kprintf("\n");
       }
   #endif
   
       /*
        * Clear the originating core from our ipimask, we will process all
        * incoming messages.
        *
        * Obtain the current write index, which is modified by a remote cpu.
        * Issue a load fence to prevent speculative reads of e.g. data written
        * by the other cpu prior to it updating the index.
        */
       KKASSERT(curthread->td_critcount);
       wi = ip->ip_windex;
       cpu_lfence();
       ++mygd->gd_intr_nesting_level;
   
       /*
        * NOTE: xindex is only updated after we are sure the function has
        *       finished execution.  Beware lwkt_process_ipiq() reentrancy!
        *       The function may send an IPI which may block/drain.
        *
        * NOTE: Due to additional IPI operations that the callback function
        *       may make, it is possible for both rindex and windex to advance and
        *       thus for rindex to advance passed our cached windex.
        *
        * NOTE: A load fence is required to prevent speculative loads prior
        *       to the loading of ip_rindex.  Even though stores might be
        *       ordered, loads are probably not.  A memory fence is required
        *       to prevent reordering of the loads after the ip_rindex update.
        *
        * NOTE: Single pass only.  Returns non-zero if the queue is not empty
        *       on return.
        */
       while (wi - (ri = ip->ip_rindex) > 0) {
           ri &= MAXCPUFIFO_MASK;
           cpu_lfence();
           copy_func = ip->ip_info[ri].func;
           copy_arg1 = ip->ip_info[ri].arg1;
           copy_arg2 = ip->ip_info[ri].arg2;
           cpu_mfence();
           ++ip->ip_rindex;
           KKASSERT((ip->ip_rindex & MAXCPUFIFO_MASK) ==
                    ((ri + 1) & MAXCPUFIFO_MASK));
           logipiq(receive, copy_func, copy_arg1, copy_arg2, sgd, mycpu);
   #ifdef INVARIANTS
           if (ipiq_debug && (ip->ip_rindex & 0xFFFFFF) == 0) {
                   kprintf("cpu %d ipifunc %p %p %d (frame %p)\n",
                           mycpu->gd_cpuid,
                           copy_func, copy_arg1, copy_arg2,
   #if defined(__i386__)
                           (frame ? (void *)frame->if_eip : NULL));
   #elif defined(__x86_64__)
                           (frame ? (void *)frame->if_rip : NULL));
   #else
                           NULL);
   #endif
           }
   #endif
           copy_func(copy_arg1, copy_arg2, frame);
           cpu_sfence();
           ip->ip_xindex = ip->ip_rindex;
   
   #ifdef PANIC_DEBUG
           /*
            * Simulate panics during the processing of an IPI
            */
           if (mycpu->gd_cpuid == panic_ipiq_cpu && panic_ipiq_count) {
                   if (--panic_ipiq_count == 0) {
   #ifdef DDB
                           Debugger("PANIC_DEBUG");
   #else
                           panic("PANIC_DEBUG");
   #endif
                   }
           }
   #endif
       }
       --mygd->gd_intr_nesting_level;
   
       /*
        * Return non-zero if there is still more in the queue.
        */
       cpu_lfence();
       return (ip->ip_rindex != ip->ip_windex);
   }
   
   static void
   lwkt_sync_ipiq(void *arg)
   {
       volatile cpumask_t *cpumask = arg;
   
       atomic_clear_cpumask(cpumask, mycpu->gd_cpumask);
       if (*cpumask == 0)
           wakeup(cpumask);
   }
   
   void
   lwkt_synchronize_ipiqs(const char *wmesg)
   {
       volatile cpumask_t other_cpumask;
   
       other_cpumask = mycpu->gd_other_cpus & smp_active_mask;
       lwkt_send_ipiq_mask(other_cpumask, lwkt_sync_ipiq,
           __DEVOLATILE(void *, &other_cpumask));
   
       while (other_cpumask != 0) {
           tsleep_interlock(&other_cpumask, 0);
           if (other_cpumask != 0)
               tsleep(&other_cpumask, PINTERLOCKED, wmesg, 0);
       }
   }
   
   /*
    * CPU Synchronization Support
    *
    * lwkt_cpusync_interlock()     - Place specified cpus in a quiescent state.
    *                                The current cpu is placed in a hard critical
    *                                section.
    *
    * lwkt_cpusync_deinterlock()   - Execute cs_func on specified cpus, including
    *                                current cpu if specified, then return.
    */
   void
   lwkt_cpusync_simple(cpumask_t mask, cpusync_func_t func, void *arg)
   {
       struct lwkt_cpusync cs;
   
       lwkt_cpusync_init(&cs, mask, func, arg);
       lwkt_cpusync_interlock(&cs);
       lwkt_cpusync_deinterlock(&cs);
   }
   
   
   void
   lwkt_cpusync_interlock(lwkt_cpusync_t cs)
   {
   #if 0
       const char *smsg = "SMPSYNL";
   #endif
       globaldata_t gd = mycpu;
       cpumask_t mask;
   
       /*
        * mask acknowledge (cs_mack):  0->mask for stage 1
        *
        * mack does not include the current cpu.
        */
       mask = cs->cs_mask & gd->gd_other_cpus & smp_active_mask;
       cs->cs_mack = 0;
       crit_enter_id("cpusync");
       if (mask) {
           DEBUG_PUSH_INFO("cpusync_interlock");
           ++ipiq_stat(gd).ipiq_cscount;
           ++gd->gd_curthread->td_cscount;
           lwkt_send_ipiq_mask(mask, (ipifunc1_t)lwkt_cpusync_remote1, cs);
           logipiq2(sync_start, (long)mask);
   #if 0
           if (gd->gd_curthread->td_wmesg == NULL)
                   gd->gd_curthread->td_wmesg = smsg;
   #endif
           while (cs->cs_mack != mask) {
               lwkt_process_ipiq();
               cpu_pause();
   #ifdef _KERNEL_VIRTUAL
               pthread_yield();
   #endif
           }
   #if 0
           if (gd->gd_curthread->td_wmesg == smsg)
                   gd->gd_curthread->td_wmesg = NULL;
   #endif
           DEBUG_POP_INFO();
       }
   }
   
   /*
    * Interlocked cpus have executed remote1 and are polling in remote2.
    * To deinterlock we clear cs_mack and wait for the cpus to execute
    * the func and set their bit in cs_mack again.
    *
    */
   void
   lwkt_cpusync_deinterlock(lwkt_cpusync_t cs)
   {
       globaldata_t gd = mycpu;
   #if 0
       const char *smsg = "SMPSYNU";
   #endif
       cpumask_t mask;
   
       /*
        * mask acknowledge (cs_mack):  mack->0->mack for stage 2
        *
        * Clearing cpu bits for polling cpus in cs_mack will cause them to
        * execute stage 2, which executes the cs_func(cs_data) and then sets
        * their bit in cs_mack again.
        *
        * mack does not include the current cpu.
        */
       mask = cs->cs_mack;
       cpu_ccfence();
       cs->cs_mack = 0;
       cpu_ccfence();
       if (cs->cs_func && (cs->cs_mask & gd->gd_cpumask))
               cs->cs_func(cs->cs_data);
       if (mask) {
           DEBUG_PUSH_INFO("cpusync_deinterlock");
   #if 0
           if (gd->gd_curthread->td_wmesg == NULL)
                   gd->gd_curthread->td_wmesg = smsg;
   #endif
           while (cs->cs_mack != mask) {
               lwkt_process_ipiq();
               cpu_pause();
   #ifdef _KERNEL_VIRTUAL
               pthread_yield();
   #endif
           }
   #if 0
           if (gd->gd_curthread->td_wmesg == smsg)
                   gd->gd_curthread->td_wmesg = NULL;
   #endif
           DEBUG_POP_INFO();
           /*
            * cpusyncq ipis may be left queued without the RQF flag set due to
            * a non-zero td_cscount, so be sure to process any laggards after
            * decrementing td_cscount.
            */
           --gd->gd_curthread->td_cscount;
           lwkt_process_ipiq();
           logipiq2(sync_end, (long)mask);
       }
       crit_exit_id("cpusync");
   }
   
   /*
    * helper IPI remote messaging function.
    * 
    * Called on remote cpu when a new cpu synchronization request has been
    * sent to us.  Execute the run function and adjust cs_count, then requeue
    * the request so we spin on it.
    */
   static void
   lwkt_cpusync_remote1(lwkt_cpusync_t cs)
   {
       globaldata_t gd = mycpu;
   
       atomic_set_cpumask(&cs->cs_mack, gd->gd_cpumask);
       lwkt_cpusync_remote2(cs);
   }
   
   /*
    * helper IPI remote messaging function.
    *
    * Poll for the originator telling us to finish.  If it hasn't, requeue
    * our request so we spin on it.
    */
   static void
   lwkt_cpusync_remote2(lwkt_cpusync_t cs)
   {
       globaldata_t gd = mycpu;
   
       if ((cs->cs_mack & gd->gd_cpumask) == 0) {
           if (cs->cs_func)
                   cs->cs_func(cs->cs_data);
           atomic_set_cpumask(&cs->cs_mack, gd->gd_cpumask);
           /* cs can be ripped out at this point */
       } else {
           lwkt_ipiq_t ip;
           int wi;
   
   #ifdef _KERNEL_VIRTUAL
           pthread_yield();
   #endif
           ip = &gd->gd_cpusyncq;
           wi = ip->ip_windex & MAXCPUFIFO_MASK;
           ip->ip_info[wi].func = (ipifunc3_t)(ipifunc1_t)lwkt_cpusync_remote2;
           ip->ip_info[wi].arg1 = cs;
           ip->ip_info[wi].arg2 = 0;
           cpu_sfence();
           KKASSERT(ip->ip_windex - ip->ip_rindex < MAXCPUFIFO);
           ++ip->ip_windex;
           if (ipiq_debug && (ip->ip_windex & 0xFFFFFF) == 0) {
                   kprintf("cpu %d cm=%016jx %016jx f=%p\n",
                           gd->gd_cpuid,
                           (intmax_t)cs->cs_mask, (intmax_t)cs->cs_mack,
                           cs->cs_func);
           }
       }
   }

Cache object: f8a12d2be23dc62c95701e8fa1f2b031