From mboxrd@z Thu Jan 1 00:00:00 1970 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 From: Stefan Hajnoczi 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> Subject: [Qemu-devel] [PATCH 13/28] qcow2: drop flush in update_cluster_refcount() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Anthony Liguori 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); } -- 1.8.1.4