From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60022) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YGYlz-0004Hr-Q8 for qemu-devel@nongnu.org; Wed, 28 Jan 2015 14:59:36 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YGYlu-0008T4-3z for qemu-devel@nongnu.org; Wed, 28 Jan 2015 14:59:35 -0500 Received: from mx2.parallels.com ([199.115.105.18]:42341) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YGYlt-0008Sy-Op for qemu-devel@nongnu.org; Wed, 28 Jan 2015 14:59:30 -0500 Message-ID: <54C93F98.1030006@openvz.org> Date: Wed, 28 Jan 2015 22:59:20 +0300 From: "Denis V. Lunev" MIME-Version: 1.0 References: <1422470996-20820-1-git-send-email-den@openvz.org> <1422470996-20820-2-git-send-email-den@openvz.org> In-Reply-To: <1422470996-20820-2-git-send-email-den@openvz.org> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/1] block: change default memory alignment for block requests to 4096 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , qemu-devel@nongnu.org, Stefan Hajnoczi On 28/01/15 21:49, Denis V. Lunev wrote: > The following sequence > int fd = open(argv[1], O_RDWR | O_CREAT | O_DIRECT, 0644); > for (i = 0; i < 100000; i++) > write(fd, buf, 4096); > performs 10% better if buf is aligned to 4096 bytes rather then to > 512 bytes on HDD with 512/4096 logical/physical sector size. > > The difference is quite reliable. > > Signed-off-by: Denis V. Lunev > CC: Kevin Wolf > CC: Stefan Hajnoczi > --- > block.c | 4 ++-- > block/raw-posix.c | 4 ++-- > 2 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/block.c b/block.c > index d45e4dd..bc5d1e7 100644 > --- a/block.c > +++ b/block.c > @@ -543,7 +543,7 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp) > bs->bl.max_transfer_length = bs->file->bl.max_transfer_length; > bs->bl.opt_mem_alignment = bs->file->bl.opt_mem_alignment; > } else { > - bs->bl.opt_mem_alignment = 512; > + bs->bl.opt_mem_alignment = 4096; > } > > if (bs->backing_hd) { > @@ -966,7 +966,7 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file, > > bs->open_flags = flags; > bs->guest_block_size = 512; > - bs->request_alignment = 512; > + bs->request_alignment = 4096; > bs->zero_beyond_eof = true; > open_flags = bdrv_open_flags(bs, flags); > bs->read_only = !(open_flags & BDRV_O_RDWR); > diff --git a/block/raw-posix.c b/block/raw-posix.c > index ec38fee..d1b3388 100644 > --- a/block/raw-posix.c > +++ b/block/raw-posix.c > @@ -266,7 +266,7 @@ static void raw_probe_alignment(BlockDriverState *bs, int fd, Error **errp) > if (!s->buf_align) { > size_t align; > buf = qemu_memalign(MAX_BLOCKSIZE, 2 * MAX_BLOCKSIZE); > - for (align = 512; align <= MAX_BLOCKSIZE; align <<= 1) { > + for (align = 4096; align <= MAX_BLOCKSIZE; align <<= 1) { > if (pread(fd, buf + align, MAX_BLOCKSIZE, 0) >= 0) { > s->buf_align = align; > break; > @@ -278,7 +278,7 @@ static void raw_probe_alignment(BlockDriverState *bs, int fd, Error **errp) > if (!bs->request_alignment) { > size_t align; > buf = qemu_memalign(s->buf_align, MAX_BLOCKSIZE); > - for (align = 512; align <= MAX_BLOCKSIZE; align <<= 1) { > + for (align = 4096; align <= MAX_BLOCKSIZE; align <<= 1) { > if (pread(fd, buf, align, 0) >= 0) { > bs->request_alignment = align; > break; sorry, the patch is wrong. It breaks 'make check-block'. I will redo it and perform more testing. request-alignment related changes are wrong :( I have run tests without them but added them as a obvious last minute addition.