From: Kevin Wolf <kwolf@redhat.com>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: qemu-devel@nongnu.org, hch@lst.de
Subject: [Qemu-devel] Re: [RFC][PATCH 2/2] qcow2: Use bdrv_(p)write_sync for metadata writes
Date: Thu, 17 Jun 2010 16:39:54 +0200 [thread overview]
Message-ID: <4C1A33BA.4030303@redhat.com> (raw)
In-Reply-To: <AANLkTimhkfNhuiuJOy21yOOfyQXomFR1OPAHAt7vM23N@mail.gmail.com>
Am 17.06.2010 16:19, schrieb Stefan Hajnoczi:
> On Thu, Jun 17, 2010 at 1:03 PM, Kevin Wolf <kwolf@redhat.com> wrote:
>> Use bdrv_(p)write_sync to ensure metadata integrity in case of a crash.
>
> Any performance numbers? This change is necessary for correctness but
> I wonder what the performance impact is for users.
No numbers yet, but as you say we need to do it anyway. It should
definitely be better than any other option that I can think of
(cache=writethrough or some O_DIRECT|O_DSYNC mode) in that it only hurts
performance when metadata is actually changed. As long as we only write
guest data, there is no difference.
Making it a barrier instead of a flush would probably be better, have
you already had a look at this since we talked about it?
Kevin
next prev parent reply other threads:[~2010-06-17 14:40 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-17 12:03 [Qemu-devel] [RFC][PATCH 0/2] block: Add flush after metadata writes Kevin Wolf
2010-06-17 12:03 ` [Qemu-devel] [RFC][PATCH 1/2] block: Add bdrv_(p)write_sync Kevin Wolf
2010-06-17 12:03 ` [Qemu-devel] [RFC][PATCH 2/2] qcow2: Use bdrv_(p)write_sync for metadata writes Kevin Wolf
2010-06-17 14:19 ` [Qemu-devel] " Stefan Hajnoczi
2010-06-17 14:39 ` Kevin Wolf [this message]
2010-06-17 19:47 ` Stefan Hajnoczi
2010-06-18 7:54 ` Kevin Wolf
2010-06-18 7:58 ` Christoph Hellwig
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