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![Peter Lieven](/assets/img/avatar_default.png)
Placing coroutines on the global pool should be preferrable, because it can help all threads. But if the global pool is full, we can still try to save some allocations by stashing completed coroutines on the local pool. This is quite cheap too, because it does not require atomic operations, and provides a gain of 15% in the best case. Signed-off-by: Peter Lieven <pl@kamp.de> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Fam Zheng <famz@redhat.com> Message-id: 1417518350-6167-8-git-send-email-pbonzini@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
153 lines
3.9 KiB
C
153 lines
3.9 KiB
C
/*
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* QEMU coroutines
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*
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* Copyright IBM, Corp. 2011
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*
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* Authors:
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* Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
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* Kevin Wolf <kwolf@redhat.com>
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*
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* This work is licensed under the terms of the GNU LGPL, version 2 or later.
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* See the COPYING.LIB file in the top-level directory.
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*
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*/
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#include "trace.h"
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#include "qemu-common.h"
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#include "qemu/thread.h"
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#include "qemu/atomic.h"
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#include "block/coroutine.h"
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#include "block/coroutine_int.h"
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enum {
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POOL_BATCH_SIZE = 64,
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};
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/** Free list to speed up creation */
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static QSLIST_HEAD(, Coroutine) release_pool = QSLIST_HEAD_INITIALIZER(pool);
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static unsigned int release_pool_size;
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static __thread QSLIST_HEAD(, Coroutine) alloc_pool = QSLIST_HEAD_INITIALIZER(pool);
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static __thread unsigned int alloc_pool_size;
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static __thread Notifier coroutine_pool_cleanup_notifier;
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static void coroutine_pool_cleanup(Notifier *n, void *value)
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{
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Coroutine *co;
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Coroutine *tmp;
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QSLIST_FOREACH_SAFE(co, &alloc_pool, pool_next, tmp) {
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QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
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qemu_coroutine_delete(co);
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}
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}
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Coroutine *qemu_coroutine_create(CoroutineEntry *entry)
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{
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Coroutine *co = NULL;
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if (CONFIG_COROUTINE_POOL) {
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co = QSLIST_FIRST(&alloc_pool);
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if (!co) {
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if (release_pool_size > POOL_BATCH_SIZE) {
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/* Slow path; a good place to register the destructor, too. */
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if (!coroutine_pool_cleanup_notifier.notify) {
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coroutine_pool_cleanup_notifier.notify = coroutine_pool_cleanup;
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qemu_thread_atexit_add(&coroutine_pool_cleanup_notifier);
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}
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/* This is not exact; there could be a little skew between
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* release_pool_size and the actual size of release_pool. But
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* it is just a heuristic, it does not need to be perfect.
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*/
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alloc_pool_size = atomic_xchg(&release_pool_size, 0);
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QSLIST_MOVE_ATOMIC(&alloc_pool, &release_pool);
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co = QSLIST_FIRST(&alloc_pool);
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}
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}
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if (co) {
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QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
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alloc_pool_size--;
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}
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}
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if (!co) {
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co = qemu_coroutine_new();
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}
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co->entry = entry;
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QTAILQ_INIT(&co->co_queue_wakeup);
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return co;
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}
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static void coroutine_delete(Coroutine *co)
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{
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co->caller = NULL;
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if (CONFIG_COROUTINE_POOL) {
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if (release_pool_size < POOL_BATCH_SIZE * 2) {
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QSLIST_INSERT_HEAD_ATOMIC(&release_pool, co, pool_next);
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atomic_inc(&release_pool_size);
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return;
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}
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if (alloc_pool_size < POOL_BATCH_SIZE) {
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QSLIST_INSERT_HEAD(&alloc_pool, co, pool_next);
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alloc_pool_size++;
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return;
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}
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}
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qemu_coroutine_delete(co);
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}
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static void coroutine_swap(Coroutine *from, Coroutine *to)
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{
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CoroutineAction ret;
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ret = qemu_coroutine_switch(from, to, COROUTINE_YIELD);
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qemu_co_queue_run_restart(to);
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switch (ret) {
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case COROUTINE_YIELD:
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return;
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case COROUTINE_TERMINATE:
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trace_qemu_coroutine_terminate(to);
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coroutine_delete(to);
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return;
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default:
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abort();
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}
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}
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void qemu_coroutine_enter(Coroutine *co, void *opaque)
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{
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Coroutine *self = qemu_coroutine_self();
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trace_qemu_coroutine_enter(self, co, opaque);
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if (co->caller) {
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fprintf(stderr, "Co-routine re-entered recursively\n");
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abort();
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}
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co->caller = self;
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co->entry_arg = opaque;
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coroutine_swap(self, co);
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}
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void coroutine_fn qemu_coroutine_yield(void)
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{
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Coroutine *self = qemu_coroutine_self();
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Coroutine *to = self->caller;
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trace_qemu_coroutine_yield(self, to);
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if (!to) {
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fprintf(stderr, "Co-routine is yielding to no one\n");
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abort();
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}
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self->caller = NULL;
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coroutine_swap(self, to);
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}
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