From patchwork Thu Jun 2 15:58:15 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Denis V. Lunev" X-Patchwork-Id: 629363 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 3rLCk20c8bz9t6n for ; Fri, 3 Jun 2016 02:44:26 +1000 (AEST) Received: from localhost ([::1]:48874 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b8VjM-0002RM-5J for incoming@patchwork.ozlabs.org; Thu, 02 Jun 2016 12:44:24 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46902) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b8V11-0003OC-Ph for qemu-devel@nongnu.org; Thu, 02 Jun 2016 11:58:36 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b8V0x-0003zB-Lt for qemu-devel@nongnu.org; Thu, 02 Jun 2016 11:58:35 -0400 Received: from mailhub.sw.ru ([195.214.232.25]:42503 helo=relay.sw.ru) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b8V0x-0003pQ-7M; Thu, 02 Jun 2016 11:58:31 -0400 Received: from irbis.sw.ru ([10.30.2.139]) by relay.sw.ru (8.13.4/8.13.4) with ESMTP id u52FwFMh014107; Thu, 2 Jun 2016 18:58:17 +0300 (MSK) From: "Denis V. Lunev" To: qemu-block@nongnu.org, qemu-devel@nongnu.org Date: Thu, 2 Jun 2016 18:58:15 +0300 Message-Id: <1464883095-6285-1-git-send-email-den@openvz.org> X-Mailer: git-send-email 2.1.4 X-detected-operating-system: by eggs.gnu.org: OpenBSD 3.x X-Received-From: 195.214.232.25 Subject: [Qemu-devel] [PATCH 1/1] qcow2: avoid extra flushes in qcow2 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , den@openvz.org, Pavel Borzenkov , Max Reitz Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" The problem with excessive flushing was found by a couple of performance tests: - parallel directory tree creation (from 2 processes) - 32 cached writes + fsync at the end in a loop For the first one results improved from 2.6 loops/sec to 3.5 loops/sec. Each loop creates 10^3 directories with 10 files in each. For the second one results improved from ~600 fsync/sec to ~1100 fsync/sec. Though, it was run on SSD so it probably won't show such performance gain on rotational media. 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. These flushes are necessary to keep the right order of writes to the different caches. Though this is not necessary in the current code base as this ordering is ensured through the flush in qcow2_cache_flush_dependency(). Signed-off-by: Denis V. Lunev CC: Pavel Borzenkov CC: Kevin Wolf CC: Max Reitz --- Changes from v1: - renamed qcow2_cache_flush_nosync to qcow2_cache_write (looks better to me) - rewritten commit message entirely 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..208a060 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_write(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_write(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..a194a8a 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_write(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_write(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..7db9795 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_write(BlockDriverState *bs, Qcow2Cache *c); int qcow2_cache_set_dependency(BlockDriverState *bs, Qcow2Cache *c, Qcow2Cache *dependency); void qcow2_cache_depends_on_flush(Qcow2Cache *c);