Re: [Qemu-devel] converting the block layer from coroutines to threads

[Anthony Liguori]

On 02/24/2012 01:02 PM, Paolo Bonzini wrote:
> Hi all,
>
> a few weeks ago Stefan Hajnoczi pointed me to his work on virtio-blk
> performance.
>
> Stefan's work had two sides.  First, he captured very nice performance
> data of the block layer at
> http://www.linux-kvm.org/page/Virtio/Block/Latency; second, in order to
> measure peak performance, he basically implemented "vhost-blk" in
> userspace.

I don't think the improvements here have anything to do with the block layer.

We've done the same thing with virtio-net and saw impressive performance results 
as a consequence.  Conversely, we see a similar improvement by applying the same 
technique to vhost-net.

Virtio really wants each virtqueue to be processed in a separate thread.  On a 
multicore system, there's considerable improvement doing this.

I think that's where we ought to start.  We really just need the block layer to 
be re-entrant, we don't actually need qcow2 or anything else that uses 
coroutines to use full threads.

Or at least, as far as I know, we don't have any performance data to suggest 
that we do.

Regards,

Anthony Liguori