Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2

[Ming Lei]

On Fri, Jun 27, 2014 at 12:59 PM, Paolo Bonzini <address@hidden> wrote:
> Il 27/06/2014 03:15, Ming Lei ha scritto:
>>
>> On Thu, Jun 26, 2014 at 11:57 PM, Paolo Bonzini <address@hidden>
>> wrote:
>>>
>>> We can implement (advisory) calls like bdrv_plug/bdrv_unplug in order to
>>> restore the previous levels of performance.
>>
>>
>> Yes, that is also what I am thinking, or interfaces like bdrv_queue_io()
>> and bdrv_submit_io(), which may match with aio interfaces.
>
>
> Would you like to try preparing a patch?

OK, let me try to do that.

>
>
>>>
>>> Note that some fallout of the conversion was expected.  Dataplane told us
>>> experimentally what level of performance could be reached, but was a dead
>>> end in terms of functionality.  Now Stefan added a whole lot of
>>> functionality to dataplane (accounting, throttling, file formats and
>>> protocols, thread-pool based I/O, etc.) and we need to bring back any
>>> performance we lost in the process.
>>
>>
>> These features are very good, but looks the conversion is a bit early, :-(
>
>
> Dataplane is still (and has always been) experimental.  For now, it's a
> playground to get rid of the big QEMU lock in hot paths.  As such,
> performance going up and down is expected.  The good thing is that every
> performance improvement we do now will not be restricted to dataplane, it
> can be applied just as well to any other device.

Yes, virtio-scsi may benefit from the improvement too, and other
block devices too.


Thanks,
-- 
Ming Lei