From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54282) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a1Hv3-0001Mc-MY for qemu-devel@nongnu.org; Tue, 24 Nov 2015 13:02:22 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1a1Hv2-0005ye-4P for qemu-devel@nongnu.org; Tue, 24 Nov 2015 13:02:21 -0500 From: Paolo Bonzini Date: Tue, 24 Nov 2015 19:01:13 +0100 Message-Id: <1448388091-117282-23-git-send-email-pbonzini@redhat.com> In-Reply-To: <1448388091-117282-1-git-send-email-pbonzini@redhat.com> References: <1448388091-117282-1-git-send-email-pbonzini@redhat.com> Subject: [Qemu-devel] [PATCH 22/40] aio: make ctx->list_lock a QemuLockCnt, subsuming ctx->walking_bh List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org, qemu-block@nongnu.org This will make it possible to walk the list of bottom halves without holding the AioContext lock---and in turn to call bottom half handlers without holding the lock. Signed-off-by: Paolo Bonzini --- async.c | 31 ++++++++++++++----------------- include/block/aio.h | 12 +++++------- 2 files changed, 19 insertions(+), 24 deletions(-) diff --git a/async.c b/async.c index 7015bad..4c1f658 100644 --- a/async.c +++ b/async.c @@ -50,12 +50,12 @@ QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque) .cb = cb, .opaque = opaque, }; - qemu_mutex_lock(&ctx->list_lock); + qemu_lockcnt_lock(&ctx->list_lock); bh->next = ctx->first_bh; /* Make sure that the members are ready before putting bh into list */ smp_wmb(); ctx->first_bh = bh; - qemu_mutex_unlock(&ctx->list_lock); + qemu_lockcnt_unlock(&ctx->list_lock); return bh; } @@ -70,13 +70,11 @@ int aio_bh_poll(AioContext *ctx) QEMUBH *bh, **bhp, *next; int ret; - ctx->walking_bh++; + qemu_lockcnt_inc(&ctx->list_lock); ret = 0; - for (bh = ctx->first_bh; bh; bh = next) { - /* Make sure that fetching bh happens before accessing its members */ - smp_read_barrier_depends(); - next = bh->next; + for (bh = atomic_rcu_read(&ctx->first_bh); bh; bh = next) { + next = atomic_rcu_read(&bh->next); /* The atomic_xchg is paired with the one in qemu_bh_schedule. The * implicit memory barrier ensures that the callback sees all writes * done by the scheduling thread. It also ensures that the scheduling @@ -93,11 +91,8 @@ int aio_bh_poll(AioContext *ctx) } } - ctx->walking_bh--; - /* remove deleted bhs */ - if (!ctx->walking_bh) { - qemu_mutex_lock(&ctx->list_lock); + if (qemu_lockcnt_dec_and_lock(&ctx->list_lock)) { bhp = &ctx->first_bh; while (*bhp) { bh = *bhp; @@ -108,7 +103,7 @@ int aio_bh_poll(AioContext *ctx) bhp = &bh->next; } } - qemu_mutex_unlock(&ctx->list_lock); + qemu_lockcnt_unlock(&ctx->list_lock); } return ret; @@ -164,7 +159,8 @@ aio_compute_timeout(AioContext *ctx) int timeout = -1; QEMUBH *bh; - for (bh = ctx->first_bh; bh; bh = bh->next) { + for (bh = atomic_rcu_read(&ctx->first_bh); bh; + bh = atomic_rcu_read(&bh->next)) { if (!bh->deleted && bh->scheduled) { if (bh->idle) { /* idle bottom halves will be polled at least @@ -239,7 +235,8 @@ aio_ctx_finalize(GSource *source) thread_pool_free(ctx->thread_pool); - qemu_mutex_lock(&ctx->list_lock); + qemu_lockcnt_lock(&ctx->list_lock); + assert(!qemu_lockcnt_count(&ctx->list_lock)); while (ctx->first_bh) { QEMUBH *next = ctx->first_bh->next; @@ -249,12 +246,12 @@ aio_ctx_finalize(GSource *source) g_free(ctx->first_bh); ctx->first_bh = next; } - qemu_mutex_unlock(&ctx->list_lock); + qemu_lockcnt_unlock(&ctx->list_lock); aio_set_event_notifier(ctx, &ctx->notifier, false, NULL); event_notifier_cleanup(&ctx->notifier); qemu_rec_mutex_destroy(&ctx->lock); - qemu_mutex_destroy(&ctx->list_lock); + qemu_lockcnt_destroy(&ctx->list_lock); timerlistgroup_deinit(&ctx->tlg); } @@ -330,7 +327,7 @@ AioContext *aio_context_new(Error **errp) (EventNotifierHandler *) event_notifier_dummy_cb); ctx->thread_pool = NULL; - qemu_mutex_init(&ctx->list_lock); + qemu_lockcnt_init(&ctx->list_lock); qemu_rec_mutex_init(&ctx->lock); timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx); diff --git a/include/block/aio.h b/include/block/aio.h index 5d60d68..26aa658 100644 --- a/include/block/aio.h +++ b/include/block/aio.h @@ -87,17 +87,15 @@ struct AioContext { */ uint32_t notify_me; - /* lock to protect between bh's adders and deleter */ - QemuMutex list_lock; + /* A lock to protect between bh's adders and deleter, and to ensure + * that no callbacks are removed while we're walking and dispatching + * them. + */ + QemuLockCnt list_lock; /* Anchor of the list of Bottom Halves belonging to the context */ struct QEMUBH *first_bh; - /* A simple lock used to protect the first_bh list, and ensure that - * no callbacks are removed while we're walking and dispatching callbacks. - */ - int walking_bh; - /* Used by aio_notify. * * "notified" is used to avoid expensive event_notifier_test_and_clear -- 1.8.3.1