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/*
* QEMU coroutines
*
* Copyright IBM, Corp. 2011
*
* Authors:
* Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
* Kevin Wolf <kwolf@redhat.com>
*
* This work is licensed under the terms of the GNU LGPL, version 2 or later.
* See the COPYING.LIB file in the top-level directory.
*
*/
#include "qemu/osdep.h"
#include "trace.h"
#include "qemu/thread.h"
#include "qemu/atomic.h"
#include "qemu/coroutine.h"
#include "qemu/coroutine_int.h"
#include "block/aio.h"
/** Initial batch size is 64, and is increased on demand */
enum {
POOL_INITIAL_BATCH_SIZE = 64,
};
/** Free list to speed up creation */
static QSLIST_HEAD(, Coroutine) release_pool = QSLIST_HEAD_INITIALIZER(pool);
static unsigned int pool_batch_size = POOL_INITIAL_BATCH_SIZE;
static unsigned int release_pool_size;
static __thread QSLIST_HEAD(, Coroutine) alloc_pool = QSLIST_HEAD_INITIALIZER(pool);
static __thread unsigned int alloc_pool_size;
static __thread Notifier coroutine_pool_cleanup_notifier;
static void coroutine_pool_cleanup(Notifier *n, void *value)
{
Coroutine *co;
Coroutine *tmp;
QSLIST_FOREACH_SAFE(co, &alloc_pool, pool_next, tmp) {
QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
qemu_coroutine_delete(co);
}
}
Coroutine *qemu_coroutine_create(CoroutineEntry *entry, void *opaque)
{
Coroutine *co = NULL;
if (CONFIG_COROUTINE_POOL) {
co = QSLIST_FIRST(&alloc_pool);
if (!co) {
if (release_pool_size > qatomic_read(&pool_batch_size)) {
/* Slow path; a good place to register the destructor, too. */
if (!coroutine_pool_cleanup_notifier.notify) {
coroutine_pool_cleanup_notifier.notify = coroutine_pool_cleanup;
qemu_thread_atexit_add(&coroutine_pool_cleanup_notifier);
}
/* This is not exact; there could be a little skew between
* release_pool_size and the actual size of release_pool. But
* it is just a heuristic, it does not need to be perfect.
*/
alloc_pool_size = qatomic_xchg(&release_pool_size, 0);
QSLIST_MOVE_ATOMIC(&alloc_pool, &release_pool);
co = QSLIST_FIRST(&alloc_pool);
}
}
if (co) {
QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
alloc_pool_size--;
}
}
if (!co) {
co = qemu_coroutine_new();
}
co->entry = entry;
co->entry_arg = opaque;
QSIMPLEQ_INIT(&co->co_queue_wakeup);
return co;
}
static void coroutine_delete(Coroutine *co)
{
co->caller = NULL;
if (CONFIG_COROUTINE_POOL) {
if (release_pool_size < qatomic_read(&pool_batch_size) * 2) {
QSLIST_INSERT_HEAD_ATOMIC(&release_pool, co, pool_next);
qatomic_inc(&release_pool_size);
return;
}
if (alloc_pool_size < qatomic_read(&pool_batch_size)) {
QSLIST_INSERT_HEAD(&alloc_pool, co, pool_next);
alloc_pool_size++;
return;
}
}
qemu_coroutine_delete(co);
}
void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co)
{
QSIMPLEQ_HEAD(, Coroutine) pending = QSIMPLEQ_HEAD_INITIALIZER(pending);
Coroutine *from = qemu_coroutine_self();
QSIMPLEQ_INSERT_TAIL(&pending, co, co_queue_next);
/* Run co and any queued coroutines */
while (!QSIMPLEQ_EMPTY(&pending)) {
Coroutine *to = QSIMPLEQ_FIRST(&pending);
CoroutineAction ret;
/* Cannot rely on the read barrier for to in aio_co_wake(), as there are
* callers outside of aio_co_wake() */
const char *scheduled = qatomic_mb_read(&to->scheduled);
QSIMPLEQ_REMOVE_HEAD(&pending, co_queue_next);
trace_qemu_aio_coroutine_enter(ctx, from, to, to->entry_arg);
/* if the Coroutine has already been scheduled, entering it again will
* cause us to enter it twice, potentially even after the coroutine has
* been deleted */
if (scheduled) {
fprintf(stderr,
"%s: Co-routine was already scheduled in '%s'\n",
__func__, scheduled);
abort();
}
if (to->caller) {
fprintf(stderr, "Co-routine re-entered recursively\n");
abort();
}
to->caller = from;
to->ctx = ctx;
/* Store to->ctx before anything that stores to. Matches
* barrier in aio_co_wake and qemu_co_mutex_wake.
*/
smp_wmb();
ret = qemu_coroutine_switch(from, to, COROUTINE_ENTER);
/* Queued coroutines are run depth-first; previously pending coroutines
* run after those queued more recently.
*/
QSIMPLEQ_PREPEND(&pending, &to->co_queue_wakeup);
switch (ret) {
case COROUTINE_YIELD:
break;
case COROUTINE_TERMINATE:
assert(!to->locks_held);
trace_qemu_coroutine_terminate(to);
coroutine_delete(to);
break;
default:
abort();
}
}
}
void qemu_coroutine_enter(Coroutine *co)
{
qemu_aio_coroutine_enter(qemu_get_current_aio_context(), co);
}
void qemu_coroutine_enter_if_inactive(Coroutine *co)
{
if (!qemu_coroutine_entered(co)) {
qemu_coroutine_enter(co);
}
}
void coroutine_fn qemu_coroutine_yield(void)
{
Coroutine *self = qemu_coroutine_self();
Coroutine *to = self->caller;
trace_qemu_coroutine_yield(self, to);
if (!to) {
fprintf(stderr, "Co-routine is yielding to no one\n");
abort();
}
self->caller = NULL;
qemu_coroutine_switch(self, to, COROUTINE_YIELD);
}
bool qemu_coroutine_entered(Coroutine *co)
{
return co->caller;
}
AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co)
{
return co->ctx;
}
void qemu_coroutine_increase_pool_batch_size(unsigned int additional_pool_size)
{
qatomic_add(&pool_batch_size, additional_pool_size);
}
void qemu_coroutine_decrease_pool_batch_size(unsigned int removing_pool_size)
{
qatomic_sub(&pool_batch_size, removing_pool_size);
}
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