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Re: [Qemu-block] [PATCH] qed: fix bdrv_qed_drain

From: Paolo Bonzini
Subject: Re: [Qemu-block] [PATCH] qed: fix bdrv_qed_drain
Date: Mon, 7 Mar 2016 22:22:58 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0

On 07/03/2016 21:56, Stefan Hajnoczi wrote:
> I think the timer concept itself is troublesome.  A radical approach but
> limited to changing QED itself is to drop the timer and instead keep a
> timestamp for the last allocating write request.  Next time a write
> request (allocating or rewriting) is about to complete, do the flush and
> clear the need check flag as part of the write request (if 5 seconds
> have passed since the timestamp).

bdrv_qed_drain should be easy to fix in my new drain implementation,
which is based on draining the parent before the BdrvChild-ren.  It's
just troublesome in the current one which alternates flushing and draining.

I would just revert the patch that introduced bdrv_qed_drain for now,
and reintroduce it later (note however that something was messed up in
commit df9a681, "qed: Implement .bdrv_drain", 2015-11-12, because it
includes some dirty bitmap stuff).

Or perhaps the idea of making QED read-only has some merit...


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