From patchwork Fri Mar 15 15:14:10 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 228050 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 789502C00E7 for ; Sat, 16 Mar 2013 02:18:36 +1100 (EST) Received: from localhost ([::1]:51537 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UGWOw-0004pG-HH for incoming@patchwork.ozlabs.org; Fri, 15 Mar 2013 11:18:34 -0400 Received: from eggs.gnu.org ([208.118.235.92]:42997) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UGWLU-00085p-7e for qemu-devel@nongnu.org; Fri, 15 Mar 2013 11:15:06 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UGWLM-0004AG-T1 for qemu-devel@nongnu.org; Fri, 15 Mar 2013 11:15:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47991) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UGWLM-0004A7-LW for qemu-devel@nongnu.org; Fri, 15 Mar 2013 11:14:52 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id r2FFEq1T014455 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Fri, 15 Mar 2013 11:14:52 -0400 Received: from localhost (ovpn-112-50.ams2.redhat.com [10.36.112.50]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id r2FFEpSg001449; Fri, 15 Mar 2013 11:14:51 -0400 From: Stefan Hajnoczi To: Date: Fri, 15 Mar 2013 16:14:10 +0100 Message-Id: <1363360465-5247-14-git-send-email-stefanha@redhat.com> In-Reply-To: <1363360465-5247-1-git-send-email-stefanha@redhat.com> References: <1363360465-5247-1-git-send-email-stefanha@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 209.132.183.28 Cc: Anthony Liguori Subject: [Qemu-devel] [PATCH 13/28] qcow2: drop flush in update_cluster_refcount() X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org The update_cluster_refcount() function increments/decrements a cluster's refcount and then returns the new refcount value. There is no need to flush since both update_cluster_refcount() callers already take care of this: 1. qcow2_alloc_bytes() calls update_cluster_refcount() when compressed sectors will be appended to an existing cluster with enough free space. qcow2_alloc_bytes() already flushes so there is no need to do so in update_cluster_refcount(). 2. qcow2_update_snapshot_refcount() sets a cache dependency on refcounts if it needs to update L2 entries. It also flushes before completing. Removing this flush significantly speeds up qcow2 snapshot creation: $ qemu-img create -f qcow2 test.qcow2 -o size=50G,preallocation=metadata $ time qemu-img snapshot -c new test.qcow2 Time drops from more than 3 minutes to under 1 second. Signed-off-by: Stefan Hajnoczi Signed-off-by: Kevin Wolf --- block/qcow2-refcount.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index 3d29d30..92519ea 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -532,8 +532,6 @@ static int update_cluster_refcount(BlockDriverState *bs, return ret; } - bdrv_flush(bs->file); - return get_refcount(bs, cluster_index); }