From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51892) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b82CI-00017P-PK for qemu-devel@nongnu.org; Wed, 01 Jun 2016 05:12:23 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b82CE-0004UX-7N for qemu-devel@nongnu.org; Wed, 01 Jun 2016 05:12:18 -0400 Received: from mailhub.sw.ru ([195.214.232.25]:27190 helo=relay.sw.ru) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b82CD-0004Ti-Qb for qemu-devel@nongnu.org; Wed, 01 Jun 2016 05:12:14 -0400 From: "Denis V. Lunev" Date: Wed, 1 Jun 2016 12:12:04 +0300 Message-Id: <1464772324-7354-1-git-send-email-den@openvz.org> Subject: [Qemu-devel] [PATCH 1/1] qcow2: avoid extra flushes in qcow2 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-block@nongnu.org, qemu-devel@nongnu.org Cc: den@openvz.org, Pavel Borzenkov , Kevin Wolf , Max Reitz qcow2_cache_flush() calls bdrv_flush() unconditionally after writing cache entries of a particular cache. This can lead to as many as 2 additional fdatasyncs inside bdrv_flush. We can simply skip all fdatasync calls inside qcow2_co_flush_to_os as bdrv_flush for sure will do the job. This seriously affects the performance of database operations inside the guest. Signed-off-by: Denis V. Lunev CC: Pavel Borzenkov CC: Kevin Wolf CC: Max Reitz --- block/qcow2-cache.c | 11 +++++++++-- block/qcow2.c | 4 ++-- block/qcow2.h | 1 + 3 files changed, 12 insertions(+), 4 deletions(-) diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c index 0fe8eda..6079c4a 100644 --- a/block/qcow2-cache.c +++ b/block/qcow2-cache.c @@ -226,7 +226,7 @@ static int qcow2_cache_entry_flush(BlockDriverState *bs, Qcow2Cache *c, int i) return 0; } -int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c) +int qcow2_cache_flush_nosync(BlockDriverState *bs, Qcow2Cache *c) { BDRVQcow2State *s = bs->opaque; int result = 0; @@ -242,8 +242,15 @@ int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c) } } + return result; +} + +int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c) +{ + int result = qcow2_cache_flush_nosync(bs, c); + if (result == 0) { - ret = bdrv_flush(bs->file->bs); + int ret = bdrv_flush(bs->file->bs); if (ret < 0) { result = ret; } diff --git a/block/qcow2.c b/block/qcow2.c index 38caa66..bb6b788 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -2837,14 +2837,14 @@ static coroutine_fn int qcow2_co_flush_to_os(BlockDriverState *bs) int ret; qemu_co_mutex_lock(&s->lock); - ret = qcow2_cache_flush(bs, s->l2_table_cache); + ret = qcow2_cache_flush_nosync(bs, s->l2_table_cache); if (ret < 0) { qemu_co_mutex_unlock(&s->lock); return ret; } if (qcow2_need_accurate_refcounts(s)) { - ret = qcow2_cache_flush(bs, s->refcount_block_cache); + ret = qcow2_cache_flush_nosync(bs, s->refcount_block_cache); if (ret < 0) { qemu_co_mutex_unlock(&s->lock); return ret; diff --git a/block/qcow2.h b/block/qcow2.h index a063a3c..0751225 100644 --- a/block/qcow2.h +++ b/block/qcow2.h @@ -583,6 +583,7 @@ int qcow2_cache_destroy(BlockDriverState* bs, Qcow2Cache *c); void qcow2_cache_entry_mark_dirty(BlockDriverState *bs, Qcow2Cache *c, void *table); int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c); +int qcow2_cache_flush_nosync(BlockDriverState *bs, Qcow2Cache *c); int qcow2_cache_set_dependency(BlockDriverState *bs, Qcow2Cache *c, Qcow2Cache *dependency); void qcow2_cache_depends_on_flush(Qcow2Cache *c); -- 2.1.4