Re: [Qemu-devel] [PATCH for-2.1?!?] AioContext: speed up aio_notify

[Kevin Wolf <kwolf@redhat.com>]

Am 04.07.2014 um 09:27 hat Paolo Bonzini geschrieben:
> 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.

We have a rather long freeze phase this time (which I think is a good
thing). This patch fixes a regression, even if it may not be the most
important one because it is in experimental code. But I still think that
this time in the hard freeze is the right time to commit patches like
this. I would be very hesitant with such a patch like in the two weeks
before the release, but at this point I'm very open to including it.

All that requiring proper review and testing, of course. I reviewed it
and it looks good to me and Stefan seems to have reviewed it as well, so
I think it just needs a bit more testing.

Kevin