From: Stefan Hajnoczi <stefanha@gmail.com>
To: Liu Yuan <namei.unix@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
qemu-devel@nongnu.org,
MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Subject: Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics
Date: Fri, 4 Jan 2013 17:38:30 +0100 [thread overview]
Message-ID: <20130104163830.GF6310@stefanha-thinkpad.hitronhub.home> (raw)
In-Reply-To: <50E58B19.2050701@gmail.com>
On Thu, Jan 03, 2013 at 09:43:53PM +0800, Liu Yuan wrote:
> On 12/25/2012 04:45 PM, Liu Yuan wrote:
> > Well, I found setting cache=directsync will contain 'BDRV_O_CACHE_WB'.
> > Is this a bug for current master? If no, my current scheme will be the
> > only way to bypass cache of sheepdog.
>
> Ping. Can anyone confirm it is a bug that 'cache=directsync' will pass
> BDRV_O_CACHE_WB' in the flags?
Hi Yuan,
BDRV_O_NOCACHE means bypass host page cache (O_DIRECT).
BDRV_O_CACHE_WB specifies the cache semantics that the guest sees - that
means whether the disk cache is writethrough or writeback.
In other words, BDRV_O_NOCACHE is a host performance tweak while
BDRV_O_CACHE_WB changes the cache safety of the BlockDriverState. A
protocol driver like sheepdog doesn't need to look at BDRV_O_CACHE_WB
because it is implemented in block.c (see bdrv_co_do_writev() where QEMU
will flush when after each write when !bs->enable_write_cache).
Stefan
next prev parent reply other threads:[~2013-01-04 16:38 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-19 18:29 [Qemu-devel] [PATCH] sheepdog: implement direct write semantics Liu Yuan
2012-12-25 7:47 ` MORITA Kazutaka
2012-12-25 8:26 ` Liu Yuan
2012-12-25 8:45 ` Liu Yuan
2013-01-03 13:43 ` Liu Yuan
2013-01-04 16:38 ` Stefan Hajnoczi [this message]
2013-01-05 4:40 ` Liu Yuan
2013-01-05 5:29 ` Liu Yuan
2013-01-05 7:56 ` Liu Yuan
2013-01-07 12:31 ` Stefan Hajnoczi
2013-01-08 5:28 ` Liu Yuan
2013-01-07 13:23 ` Kevin Wolf
2013-01-08 5:42 ` Liu Yuan
2013-01-08 9:40 ` Stefan Hajnoczi
2013-01-08 9:45 ` Liu Yuan
2013-01-08 10:00 ` Kevin Wolf
2013-01-08 10:39 ` Liu Yuan
2013-01-08 10:51 ` Kevin Wolf
2013-01-08 11:08 ` Liu Yuan
2013-01-08 11:19 ` Kevin Wolf
2013-01-08 11:35 ` Liu Yuan
2013-01-08 12:12 ` Kevin Wolf
2013-01-08 13:18 ` Liu Yuan
2013-01-08 13:23 ` Liu Yuan
2013-01-09 10:25 ` Paolo Bonzini
2013-01-09 10:36 ` Liu Yuan
2013-01-09 10:40 ` Paolo Bonzini
2013-01-09 10:46 ` Liu Yuan
2013-01-09 10:58 ` Liu Yuan
2013-01-09 11:10 ` Paolo Bonzini
2013-01-09 12:07 ` Liu Yuan
2013-01-09 12:10 ` Liu Yuan
2013-01-09 12:16 ` Liu Yuan
2013-01-09 12:42 ` Kevin Wolf
2013-01-09 13:04 ` Liu Yuan
2013-01-09 15:10 ` Paolo Bonzini
2013-01-10 5:38 ` Liu Yuan
2013-01-11 7:52 ` MORITA Kazutaka
2013-01-11 8:07 ` Liu Yuan
2013-01-11 9:00 ` Paolo Bonzini
2013-01-11 9:04 ` Liu Yuan
2013-01-11 9:34 ` Paolo Bonzini
2013-01-11 9:38 ` Liu Yuan
2013-01-11 9:40 ` Paolo Bonzini
2013-01-11 9:32 ` Kevin Wolf
2013-01-10 15:25 ` Jamie Lokier
2013-01-10 15:31 ` Paolo Bonzini
2013-01-10 17:22 ` Jamie Lokier
2013-01-09 11:10 ` Kevin Wolf
2013-01-09 10:23 ` Paolo Bonzini
2013-01-10 15:12 ` Jamie Lokier
2013-01-10 15:21 ` Kevin Wolf
2013-01-10 8:03 ` [Qemu-devel] [PATCH v2] " Liu Yuan
2013-01-10 9:04 ` Stefan Hajnoczi
2013-01-11 7:35 ` MORITA Kazutaka
2013-01-11 9:23 ` Kevin Wolf
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