From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40286) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YGXgh-0002bF-HL for qemu-devel@nongnu.org; Wed, 28 Jan 2015 13:50:04 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YGXge-0005Yt-BD for qemu-devel@nongnu.org; Wed, 28 Jan 2015 13:50:03 -0500 Received: from mailhub.sw.ru ([195.214.232.25]:41004 helo=relay.sw.ru) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YGXgd-0005YH-Uo for qemu-devel@nongnu.org; Wed, 28 Jan 2015 13:50:00 -0500 From: "Denis V. Lunev" Date: Wed, 28 Jan 2015 21:49:56 +0300 Message-Id: <1422470996-20820-2-git-send-email-den@openvz.org> In-Reply-To: <1422470996-20820-1-git-send-email-den@openvz.org> References: <1422470996-20820-1-git-send-email-den@openvz.org> Subject: [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 , "Denis V. Lunev" , qemu-devel@nongnu.org, Stefan Hajnoczi 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; -- 1.9.1