From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41862) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b7LPx-0004KK-R6 for qemu-devel@nongnu.org; Mon, 30 May 2016 07:31:37 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b7LPi-0001QG-Oq for qemu-devel@nongnu.org; Mon, 30 May 2016 07:31:33 -0400 Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:46287 helo=mx01.kamp.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b7LPi-0001PV-Fn for qemu-devel@nongnu.org; Mon, 30 May 2016 07:31:18 -0400 From: Peter Lieven Date: Mon, 30 May 2016 13:31:13 +0200 Message-Id: <1464607873-28206-1-git-send-email-pl@kamp.de> Subject: [Qemu-devel] [PATCH V3] block/io: optimize bdrv_co_pwritev for small requests List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, famz@redhat.com, kwolf@redhat.com, stefanha@redhat.com, mreitz@redhat.com, pbonzini@redhat.com, Peter Lieven in a read-modify-write cycle a small request might cause head and tail to fall into the same aligned block. Currently QEMU reads the same block twice in this case which is not necessary. Signed-off-by: Peter Lieven --- v1->v2: following Paolos suggestions to simplify the if condition and adjusting the comment v2->v3: fix iotest 077 for requests that are within the same aligned block [Fam, Kevin] block/io.c | 8 ++++++++ tests/qemu-iotests/077 | 12 +----------- tests/qemu-iotests/077.out | 26 -------------------------- 3 files changed, 9 insertions(+), 37 deletions(-) diff --git a/block/io.c b/block/io.c index 2d832aa..0e4bb1e 100644 --- a/block/io.c +++ b/block/io.c @@ -1427,6 +1427,14 @@ int coroutine_fn bdrv_co_pwritev(BlockDriverState *bs, bytes += offset & (align - 1); offset = offset & ~(align - 1); + + /* We have read the tail already if the request is smaller + * than one aligned block. + */ + if (bytes < align) { + qemu_iovec_add(&local_qiov, head_buf + bytes, align - bytes); + bytes = align; + } } if ((offset + bytes) & (align - 1)) { diff --git a/tests/qemu-iotests/077 b/tests/qemu-iotests/077 index 4dc680b..d2d2a2d 100755 --- a/tests/qemu-iotests/077 +++ b/tests/qemu-iotests/077 @@ -60,7 +60,7 @@ EOF # Sequential RMW requests on the same physical sector off=0x1000 -for ev in "head" "after_head" "tail" "after_tail"; do +for ev in "head" "after_head"; do cat <