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Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics |
Date: |
Fri, 4 Jan 2013 17:38:30 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
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
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Liu Yuan, 2013/01/03
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics,
Stefan Hajnoczi <=
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Liu Yuan, 2013/01/04
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Kevin Wolf, 2013/01/07
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Liu Yuan, 2013/01/08
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Stefan Hajnoczi, 2013/01/08
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Liu Yuan, 2013/01/08
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Kevin Wolf, 2013/01/08