From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42731) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bNF69-00021C-LX for qemu-devel@nongnu.org; Wed, 13 Jul 2016 04:00:50 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bNF65-0007Yt-1J for qemu-devel@nongnu.org; Wed, 13 Jul 2016 04:00:49 -0400 Received: from mailhub.sw.ru ([195.214.232.25]:36773 helo=relay.sw.ru) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bNF64-0007Ya-JI for qemu-devel@nongnu.org; Wed, 13 Jul 2016 04:00:44 -0400 References: <1468316175-11522-1-git-send-email-den@openvz.org> <20160712135108.GC4478@noname.redhat.com> From: Vladimir Sementsov-Ogievskiy Message-ID: <5785F51C.8020107@virtuozzo.com> Date: Wed, 13 Jul 2016 11:00:28 +0300 MIME-Version: 1.0 In-Reply-To: <20160712135108.GC4478@noname.redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/1] mirror: double performance of the bulk stage if the disc is full List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf , "Denis V. Lunev" Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, Stefan Hajnoczi , Fam Zheng , Max Reitz , Jeff Cody , Eric Blake On 12.07.2016 16:51, Kevin Wolf wrote: > Am 12.07.2016 um 11:36 hat Denis V. Lunev geschrieben: >> From: Vladimir Sementsov-Ogievskiy >> >> Mirror can do up to 16 in-flight requests, but actually on full copy >> (the whole source disk is non-zero) in-flight is always 1. This happens >> as the request is not limited in size: the data occupies maximum available >> capacity of s->buf. >> >> The patch limits the size of the request to some artificial constant >> (1 Mb here), which is not that big or small. This effectively enables >> back parallelism in mirror code as it was designed. >> >> The result is important: the time to migrate 10 Gb disk is reduced from >> ~350 sec to 170 sec. >> >> Signed-off-by: Vladimir Sementsov-Ogievskiy >> Signed-off-by: Denis V. Lunev >> CC: Stefan Hajnoczi >> CC: Fam Zheng >> CC: Kevin Wolf >> CC: Max Reitz >> CC: Jeff Cody >> CC: Eric Blake >> --- >> block/mirror.c | 8 ++++++-- >> 1 file changed, 6 insertions(+), 2 deletions(-) >> >> diff --git a/block/mirror.c b/block/mirror.c >> index 4fe127e..53d3bcd 100644 >> --- a/block/mirror.c >> +++ b/block/mirror.c >> @@ -23,7 +23,9 @@ >> >> #define SLICE_TIME 100000000ULL /* ns */ >> #define MAX_IN_FLIGHT 16 >> -#define DEFAULT_MIRROR_BUF_SIZE (10 << 20) >> +#define MAX_IO_SECTORS ((1 << 20) >> BDRV_SECTOR_BITS) /* 1 Mb */ >> +#define DEFAULT_MIRROR_BUF_SIZE \ >> + (MAX_IN_FLIGHT * MAX_IO_SECTORS * BDRV_SECTOR_SIZE) >> >> /* The mirroring buffer is a list of granularity-sized chunks. >> * Free chunks are organized in a list. >> @@ -387,7 +389,9 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s) >> nb_chunks * sectors_per_chunk, >> &io_sectors, &file); >> if (ret < 0) { >> - io_sectors = nb_chunks * sectors_per_chunk; >> + io_sectors = MIN(nb_chunks * sectors_per_chunk, MAX_IO_SECTORS); >> + } else if (ret & BDRV_BLOCK_DATA) { >> + io_sectors = MIN(io_sectors, MAX_IO_SECTORS); >> } > Would it make sense to consider the actual buffer size? If we have > s->buf_size / 16 > 1 MB, then this is wasting buffer space. > > On the other hand, there is probably a minimum size where using a single > larger buffer performs better than two concurrent small ones. Which size > this is, is hard to tell, though. If we assume that 1 MB is a good > default (should we do some more testing to find the sweet spot?), we > could write this as: > > io_sectors = MIN(io_sectors, > MAX((s->buf_size / BDRV_SECTOR_SIZE) / MAX_IN_FLIGHT, > MAX_IO_SECTORS)) > > Kevin Ok, thanks, will resend. -- Best regards, Vladimir