Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics

[Kevin Wolf]

Am 08.01.2013 10:45, schrieb Liu Yuan:
> On 01/08/2013 05:40 PM, Stefan Hajnoczi wrote:
>> Otherwise use sheepdog writeback and let QEMU block.c decide when to
>> flush.  Never use sheepdog writethrough because it's redundant here.
> 
> I don't get it. What do you mean by 'redundant'? If we use virtio &
> sheepdog block driver, how can we specify writethrough mode for Sheepdog
> cache? Here 'writethrough' means use a pure read cache, which doesn't
> need flush at all.

A writethrough cache is equivalent to a write-back cache where each
write is followed by a flush. qemu makes sure to send these flushes, so
there is no need use Sheepdog's writethrough mode.

Kevin