util/qemu-coroutine.c

   1 /*
   2  * QEMU coroutines
   3  *
   4  * Copyright IBM, Corp. 2011
   5  *
   6  * Authors:
   7  *  Stefan Hajnoczi    <stefanha@linux.vnet.ibm.com>
   8  *  Kevin Wolf         <kwolf@redhat.com>
   9  *
  10  * This work is licensed under the terms of the GNU LGPL, version 2 or later.
  11  * See the COPYING.LIB file in the top-level directory.
  12  *
  13  */
  14
  15 #include "qemu/osdep.h"
  16 #include "trace.h"
  17 #include "qemu-common.h"
  18 #include "qemu/thread.h"
  19 #include "qemu/atomic.h"
  20 #include "qemu/coroutine.h"
  21 #include "qemu/coroutine_int.h"
  22 #include "block/aio.h"
  23
  24 enum {
  25     POOL_BATCH_SIZE = 64,
  26 };
  27
  28 /** Free list to speed up creation */
  29 static QSLIST_HEAD(, Coroutine) release_pool = QSLIST_HEAD_INITIALIZER(pool);
  30 static unsigned int release_pool_size;
  31 static __thread QSLIST_HEAD(, Coroutine) alloc_pool = QSLIST_HEAD_INITIALIZER(pool);
  32 static __thread unsigned int alloc_pool_size;
  33 static __thread Notifier coroutine_pool_cleanup_notifier;
  34
  35 static void coroutine_pool_cleanup(Notifier *n, void *value)
  36 {
  37     Coroutine *co;
  38     Coroutine *tmp;
  39
  40     QSLIST_FOREACH_SAFE(co, &alloc_pool, pool_next, tmp) {
  41         QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
  42         qemu_coroutine_delete(co);
  43     }
  44 }
  45
  46 Coroutine *qemu_coroutine_create(CoroutineEntry *entry, void *opaque)
  47 {
  48     Coroutine *co = NULL;
  49
  50     if (CONFIG_COROUTINE_POOL) {
  51         co = QSLIST_FIRST(&alloc_pool);
  52         if (!co) {
  53             if (release_pool_size > POOL_BATCH_SIZE) {
  54                 /* Slow path; a good place to register the destructor, too.  */
  55                 if (!coroutine_pool_cleanup_notifier.notify) {
  56                     coroutine_pool_cleanup_notifier.notify = coroutine_pool_cleanup;
  57                     qemu_thread_atexit_add(&coroutine_pool_cleanup_notifier);
  58                 }
  59
  60                 /* This is not exact; there could be a little skew between
  61                  * release_pool_size and the actual size of release_pool.  But
  62                  * it is just a heuristic, it does not need to be perfect.
  63                  */
  64                 alloc_pool_size = atomic_xchg(&release_pool_size, 0);
  65                 QSLIST_MOVE_ATOMIC(&alloc_pool, &release_pool);
  66                 co = QSLIST_FIRST(&alloc_pool);
  67             }
  68         }
  69         if (co) {
  70             QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
  71             alloc_pool_size--;
  72         }
  73     }
  74
  75     if (!co) {
  76         co = qemu_coroutine_new();
  77     }
  78
  79     co->entry = entry;
  80     co->entry_arg = opaque;
  81     QSIMPLEQ_INIT(&co->co_queue_wakeup);
  82     return co;
  83 }
  84
  85 static void coroutine_delete(Coroutine *co)
  86 {
  87     co->caller = NULL;
  88
  89     if (CONFIG_COROUTINE_POOL) {
  90         if (release_pool_size < POOL_BATCH_SIZE * 2) {
  91             QSLIST_INSERT_HEAD_ATOMIC(&release_pool, co, pool_next);
  92             atomic_inc(&release_pool_size);
  93             return;
  94         }
  95         if (alloc_pool_size < POOL_BATCH_SIZE) {
  96             QSLIST_INSERT_HEAD(&alloc_pool, co, pool_next);
  97             alloc_pool_size++;
  98             return;
  99         }
 100     }
 101
 102     qemu_coroutine_delete(co);
 103 }
 104
 105 void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co)
 106 {
 107     Coroutine *self = qemu_coroutine_self();
 108     CoroutineAction ret;
 109
 110     trace_qemu_aio_coroutine_enter(ctx, self, co, co->entry_arg);
 111
 112     if (co->caller) {
 113         fprintf(stderr, "Co-routine re-entered recursively\n");
 114         abort();
 115     }
 116
 117     co->caller = self;
 118     co->ctx = ctx;
 119
 120     /* Store co->ctx before anything that stores co.  Matches
 121      * barrier in aio_co_wake and qemu_co_mutex_wake.
 122      */
 123     smp_wmb();
 124
 125     ret = qemu_coroutine_switch(self, co, COROUTINE_ENTER);
 126
 127     qemu_co_queue_run_restart(co);
 128
 129     /* Beware, if ret == COROUTINE_YIELD and qemu_co_queue_run_restart()
 130      * has started any other coroutine, "co" might have been reentered
 131      * and even freed by now!  So be careful and do not touch it.
 132      */
 133
 134     switch (ret) {
 135     case COROUTINE_YIELD:
 136         return;
 137     case COROUTINE_TERMINATE:
 138         assert(!co->locks_held);
 139         trace_qemu_coroutine_terminate(co);
 140         coroutine_delete(co);
 141         return;
 142     default:
 143         abort();
 144     }
 145 }
 146
 147 void qemu_coroutine_enter(Coroutine *co)
 148 {
 149     qemu_aio_coroutine_enter(qemu_get_current_aio_context(), co);
 150 }
 151
 152 void qemu_coroutine_enter_if_inactive(Coroutine *co)
 153 {
 154     if (!qemu_coroutine_entered(co)) {
 155         qemu_coroutine_enter(co);
 156     }
 157 }
 158
 159 void coroutine_fn qemu_coroutine_yield(void)
 160 {
 161     Coroutine *self = qemu_coroutine_self();
 162     Coroutine *to = self->caller;
 163
 164     trace_qemu_coroutine_yield(self, to);
 165
 166     if (!to) {
 167         fprintf(stderr, "Co-routine is yielding to no one\n");
 168         abort();
 169     }
 170
 171     self->caller = NULL;
 172     qemu_coroutine_switch(self, to, COROUTINE_YIELD);
 173 }
 174
 175 bool qemu_coroutine_entered(Coroutine *co)
 176 {
 177     return co->caller;
 178 }