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Date: Tue, 16 Dec 2014 12:07:27 +0100
From: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20141216110727.GA27195@noname.str.redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v2 1/5] linux-aio: queue requests that
	cannot be submitted
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: ming.lei@canonical.com, pl@kamp.de, qemu-devel@nongnu.org, stefanha@redhat.com

Am 11.12.2014 um 14:52 hat Paolo Bonzini geschrieben:
> Keep a queue of requests that were not submitted; pass them to
> the kernel when a completion is reported, unless the queue is
> plugged.
> 
> The array of iocbs is rebuilt every time from scratch.  This
> avoids keeping the iocbs array and list synchronized.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Just found out that in qemu-img bench, this patch seems to cost about
5-8% for me.

An optimisation for the unplugged case would probably be easy, but that
would be cheating, as the devices that we're really interested in always
plug the queue (perhaps I should extend qemu-img bench to do that
optionally, too).

Anything clever that we can do about this? Or will we just have to live
with the fact that sending a single request is now slower than it used
to be before bdrv_plug?

Kevin