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Date: Fri, 04 Jul 2014 09:27:39 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH for-2.1?!?] AioContext: speed up aio_notify
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To: Ming Lei <ming.lei@canonical.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel <qemu-devel@nongnu.org>, Stefan Hajnoczi <stefanha@redhat.com>

Il 04/07/2014 09:23, Ming Lei ha scritto:
> I think it is good and better to go to 2.1, and it should save lots of
> write syscall.
>
> Also should regression be caused, the per thread trick may be
> resorted to, which should be simple.

If we have the "right" solution (which we do, unlike the plug/unplug 
case), and the benefit is there but limited, I don't see a reason to 
rush another patch in 2.1.

Some reasonable level of performance degradation or increased host CPU 
utilization was expected in 2.1; of course 40% is not reasonable.

> With multi virtqueue's coming for virtio-blk, it should save more, and I
> also plan to use the improved qemu bh to help merge requests from
> multi queue, without introducing extra notifier.

But virtio-blk multiqueue is 2.2 material, and so is coalescing of irqfd 
writes.  I think Kevin or Stefan should queue this patch (with the 
smp_mb optimization, IMHO) for block-next.

Paolo