From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:46892) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TTaIC-0001Cg-FI for qemu-devel@nongnu.org; Wed, 31 Oct 2012 11:33:24 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TTaI8-0005mf-C5 for qemu-devel@nongnu.org; Wed, 31 Oct 2012 11:33:20 -0400 Received: from mail-pb0-f45.google.com ([209.85.160.45]:41123) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TTaI8-0004ui-6M for qemu-devel@nongnu.org; Wed, 31 Oct 2012 11:33:16 -0400 Received: by mail-pb0-f45.google.com with SMTP id rp2so1021969pbb.4 for ; Wed, 31 Oct 2012 08:33:15 -0700 (PDT) Sender: Paolo Bonzini From: Paolo Bonzini Date: Wed, 31 Oct 2012 16:30:50 +0100 Message-Id: <1351697456-16107-34-git-send-email-pbonzini@redhat.com> In-Reply-To: <1351697456-16107-1-git-send-email-pbonzini@redhat.com> References: <1351697456-16107-1-git-send-email-pbonzini@redhat.com> Subject: [Qemu-devel] [PATCH v2 33/39] threadpool: do not take lock in event_notifier_ready List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: aliguori@us.ibm.com, stefanha@redhat.com 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 --- New patch. thread-pool.c | 19 +++++++++++++------ 1 file modificato, 13 inserzioni(+), 6 rimozioni(-) diff --git a/thread-pool.c b/thread-pool.c index 80749b7..651b324 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 { -- 1.7.12.1