From 19d092cf9ba3c01b0e22ef65c499ae7ddc28d0e8 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Wed, 31 Oct 2012 10:09:11 +0100 Subject: threadpool: do not take lock in event_notifier_ready The ordering is: worker thread consumer thread ------------------------------------------------------------------- write ret event_notifier_test_and_clear wmb() read state write state rmb() event_notifier_set read ret Signed-off-by: Paolo Bonzini --- thread-pool.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) (limited to 'thread-pool.c') diff --git a/thread-pool.c b/thread-pool.c index 80749b77e0..651b32419b 100644 --- a/thread-pool.c +++ b/thread-pool.c @@ -39,6 +39,11 @@ struct ThreadPoolElement { BlockDriverAIOCB common; ThreadPoolFunc *func; void *arg; + + /* Moving state out of THREAD_QUEUED is protected by lock. After + * that, only the worker thread can write to it. Reads and writes + * of state and ret are ordered with memory barriers. + */ enum ThreadState state; int ret; @@ -95,9 +100,12 @@ static void *worker_thread(void *unused) ret = req->func(req->arg); - qemu_mutex_lock(&lock); - req->state = THREAD_DONE; req->ret = ret; + /* Write ret before state. */ + smp_wmb(); + req->state = THREAD_DONE; + + qemu_mutex_lock(&lock); if (pending_cancellations) { qemu_cond_broadcast(&check_cancel); } @@ -162,11 +170,10 @@ restart: trace_thread_pool_complete(elem, elem->common.opaque, elem->ret); } if (elem->state == THREAD_DONE && elem->common.cb) { - qemu_mutex_lock(&lock); - int ret = elem->ret; - qemu_mutex_unlock(&lock); QLIST_REMOVE(elem, all); - elem->common.cb(elem->common.opaque, ret); + /* Read state before ret. */ + smp_rmb(); + elem->common.cb(elem->common.opaque, elem->ret); qemu_aio_release(elem); goto restart; } else { -- cgit v1.2.1