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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: |
Tue, 8 Jan 2013 10:40:25 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Tue, Jan 08, 2013 at 01:42:35PM +0800, Liu Yuan wrote:
> On 01/07/2013 09:23 PM, Kevin Wolf wrote:
> > No, and in theory they shouldn't have to care.
> >
> > Why do you want to handle writethrough semantics in the block driver
> > rather than letting qemu care for sending the right flushes?
>
> Because Sheepdog itself provide the client side cache implementation and
> we need means to get the cache hint from users when starting up the VM.
> This cache support:
> writethrough: provide a read cache for this VM, which is always
> consistent with cluster data
> writeback: provide a writeback cache for this VM, which only flush the
> dirty bits when VM send 'flush' request.
> directio: disable cache completely for this VM.
>
> Old QEMU (before v1.2) allows block drivers to get the cache flags, so
> Sheepdog can interpret these flags on its own to choose the right cache
> mode for each VM. doesn't QEMU need keep backward compatibility?
This sounds fine - it fits together with QEMU like this:
BDRV_NO_CACHE means sheepdog directio. We're disabling the client-side
sheepdog cache.
Otherwise use sheepdog writeback and let QEMU block.c decide when to
flush. Never use sheepdog writethrough because it's redundant here.
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, 2013/01/04
- 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 <=
- 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
- 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
- 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
- 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
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Liu Yuan, 2013/01/08
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Liu Yuan, 2013/01/08