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Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics
From: |
Liu Yuan |
Subject: |
Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics |
Date: |
Tue, 08 Jan 2013 19:35:47 +0800 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 |
On 01/08/2013 07:19 PM, Kevin Wolf wrote:
> I can't see a reason why it would do that. Can you bisect this?
>
Sure, bisect it is on my schedule, but I can't promise a deadline.
>>>> >>> It seems it is hard to restore into old semantics of cache flags due to
>>>> >>> new design of QEMU block layer. So will you accept that adding a
>>>> >>> 'flags'
>>>> >>> into BlockDriverState which carry the 'cache flags' from user to keep
>>>> >>> backward compatibility?
>>> >>
>>> >> No, going back to the old behaviour would break guest-toggled WCE.
>>> >>
>> >
>> > Guest-toggled WCE only works with IDE and seems that virtio-blk doesn't
>> > support it, no? And I think there are huge virtio-blk users.
> It works with virtio-blk and SCSI as well.
>
Okay, I see the code indeed support WCE but it requires Guest kernel to
support it. For the kernel doesn't support it, there is no way to
disable write cache, no?
>> > I didn't meant to break WCE. What I meant is to allow backward
>> > compatibility. For e.g, Sheepdog driver can make use of this dedicated
>> > cache flags to implement its own cache control and doesn't affect other
>> > drivers at all.
> How would you do it? With a WCE that changes during runtime the idea of
> a flag that is passed to bdrv_open() and stays valid as long as the
> BlockDriverState exists doesn't match reality any more.
I am not sure if I get it right. What I meant is allow Sheepdog to
control cache on the 'cache flags' at startup and ignore WCE on the run
time.
So you mean, if I choose witeback cache at startup, and then Guest
disable it via WCE, then block layer will never send flush request down
to Sheepdog driver?
Thanks,
Yuan
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, (continued)
- 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, 2013/01/07
- 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
- 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 <=
- 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
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Paolo Bonzini, 2013/01/09
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Liu Yuan, 2013/01/09
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Paolo Bonzini, 2013/01/09
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Liu Yuan, 2013/01/09
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Liu Yuan, 2013/01/09
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Paolo Bonzini, 2013/01/09
- Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics, Liu Yuan, 2013/01/09