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/thread.h"
  18 #include "qemu/atomic.h"
  19 #include "qemu/coroutine.h"
  20 #include "qemu/coroutine_int.h"
  21 #include "block/aio.h"
  22
  23 enum {
  24     POOL_BATCH_SIZE = 64,
  25 };
  26
  27 /** Free list to speed up creation */
  28 static QSLIST_HEAD(, Coroutine) release_pool = QSLIST_HEAD_INITIALIZER(pool);
  29 static unsigned int release_pool_size;
  30 static __thread QSLIST_HEAD(, Coroutine) alloc_pool = QSLIST_HEAD_INITIALIZER(pool);
  31 static __thread unsigned int alloc_pool_size;
  32 static __thread Notifier coroutine_pool_cleanup_notifier;
  33
  34 static void coroutine_pool_cleanup(Notifier *n, void *value)
  35 {
  36     Coroutine *co;
  37     Coroutine *tmp;
  38
  39     QSLIST_FOREACH_SAFE(co, &alloc_pool, pool_next, tmp) {
  40         QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
  41         qemu_coroutine_delete(co);
  42     }
  43 }
  44
  45 Coroutine *qemu_coroutine_create(CoroutineEntry *entry, void *opaque)
  46 {
  47     Coroutine *co = NULL;
  48
  49     if (CONFIG_COROUTINE_POOL) {
  50         co = QSLIST_FIRST(&alloc_pool);
  51         if (!co) {
  52             if (release_pool_size > POOL_BATCH_SIZE) {
  53                 /* Slow path; a good place to register the destructor, too.  */
  54                 if (!coroutine_pool_cleanup_notifier.notify) {
  55                     coroutine_pool_cleanup_notifier.notify = coroutine_pool_cleanup;
  56                     qemu_thread_atexit_add(&coroutine_pool_cleanup_notifier);
  57                 }
  58
  59                 /* This is not exact; there could be a little skew between
  60                  * release_pool_size and the actual size of release_pool.  But
  61                  * it is just a heuristic, it does not need to be perfect.
  62                  */
  63                 alloc_pool_size = qatomic_xchg(&release_pool_size, 0);
  64                 QSLIST_MOVE_ATOMIC(&alloc_pool, &release_pool);
  65                 co = QSLIST_FIRST(&alloc_pool);
  66             }
  67         }
  68         if (co) {
  69             QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
  70             alloc_pool_size--;
  71         }
  72     }
  73
  74     if (!co) {
  75         co = qemu_coroutine_new();
  76     }
  77
  78     co->entry = entry;
  79     co->entry_arg = opaque;
  80     QSIMPLEQ_INIT(&co->co_queue_wakeup);
  81     return co;
  82 }
  83
  84 static void coroutine_delete(Coroutine *co)
  85 {
  86     co->caller = NULL;
  87
  88     if (CONFIG_COROUTINE_POOL) {
  89         if (release_pool_size < POOL_BATCH_SIZE * 2) {
  90             QSLIST_INSERT_HEAD_ATOMIC(&release_pool, co, pool_next);
  91             qatomic_inc(&release_pool_size);
  92             return;
  93         }
  94         if (alloc_pool_size < POOL_BATCH_SIZE) {
  95             QSLIST_INSERT_HEAD(&alloc_pool, co, pool_next);
  96             alloc_pool_size++;
  97             return;
  98         }
  99     }
 100
 101     qemu_coroutine_delete(co);
 102 }
 103
 104 void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co)
 105 {
 106     QSIMPLEQ_HEAD(, Coroutine) pending = QSIMPLEQ_HEAD_INITIALIZER(pending);
 107     Coroutine *from = qemu_coroutine_self();
 108
 109     QSIMPLEQ_INSERT_TAIL(&pending, co, co_queue_next);
 110
 111     /* Run co and any queued coroutines */
 112     while (!QSIMPLEQ_EMPTY(&pending)) {
 113         Coroutine *to = QSIMPLEQ_FIRST(&pending);
 114         CoroutineAction ret;
 115
 116         /* Cannot rely on the read barrier for to in aio_co_wake(), as there are
 117          * callers outside of aio_co_wake() */
 118         const char *scheduled = qatomic_mb_read(&to->scheduled);
 119
 120         QSIMPLEQ_REMOVE_HEAD(&pending, co_queue_next);
 121
 122         trace_qemu_aio_coroutine_enter(ctx, from, to, to->entry_arg);
 123
 124         /* if the Coroutine has already been scheduled, entering it again will
 125          * cause us to enter it twice, potentially even after the coroutine has
 126          * been deleted */
 127         if (scheduled) {
 128             fprintf(stderr,
 129                     "%s: Co-routine was already scheduled in '%s'\n",
 130                     __func__, scheduled);
 131             abort();
 132         }
 133
 134         if (to->caller) {
 135             fprintf(stderr, "Co-routine re-entered recursively\n");
 136             abort();
 137         }
 138
 139         to->caller = from;
 140         to->ctx = ctx;
 141
 142         /* Store to->ctx before anything that stores to.  Matches
 143          * barrier in aio_co_wake and qemu_co_mutex_wake.
 144          */
 145         smp_wmb();
 146
 147         ret = qemu_coroutine_switch(from, to, COROUTINE_ENTER);
 148
 149         /* Queued coroutines are run depth-first; previously pending coroutines
 150          * run after those queued more recently.
 151          */
 152         QSIMPLEQ_PREPEND(&pending, &to->co_queue_wakeup);
 153
 154         switch (ret) {
 155         case COROUTINE_YIELD:
 156             break;
 157         case COROUTINE_TERMINATE:
 158             assert(!to->locks_held);
 159             trace_qemu_coroutine_terminate(to);
 160             coroutine_delete(to);
 161             break;
 162         default:
 163             abort();
 164         }
 165     }
 166 }
 167
 168 void qemu_coroutine_enter(Coroutine *co)
 169 {
 170     qemu_aio_coroutine_enter(qemu_get_current_aio_context(), co);
 171 }
 172
 173 void qemu_coroutine_enter_if_inactive(Coroutine *co)
 174 {
 175     if (!qemu_coroutine_entered(co)) {
 176         qemu_coroutine_enter(co);
 177     }
 178 }
 179
 180 void coroutine_fn qemu_coroutine_yield(void)
 181 {
 182     Coroutine *self = qemu_coroutine_self();
 183     Coroutine *to = self->caller;
 184
 185     trace_qemu_coroutine_yield(self, to);
 186
 187     if (!to) {
 188         fprintf(stderr, "Co-routine is yielding to no one\n");
 189         abort();
 190     }
 191
 192     self->caller = NULL;
 193     qemu_coroutine_switch(self, to, COROUTINE_YIELD);
 194 }
 195
 196 bool qemu_coroutine_entered(Coroutine *co)
 197 {
 198     return co->caller;
 199 }
 200
 201 AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co)
 202 {
 203     return co->ctx;
 204 }