Re: [Qemu-discuss] Using vhost scsi

[Michael S. Tsirkin]

On Wed, Jul 27, 2016 at 09:34:25AM +0100, Stefan Hajnoczi wrote:
> On Tue, Jul 26, 2016 at 06:35:30PM +0000, Yehuda Yitschak wrote:
> > Thanks a lot for the detailed answer 
> > 
> > I managed to run virtio-scsi and i am benchmarking the performance
> > 
> > just curios, does virtio-scsi deliver about the same performance as 
> > vhost-scsi ? 
> 
> Both virtio-scsi and vhost-scsi support many different configurations.
> If achieving the best performance is critical then you need to benchmark
> them yourself.
> 
> > i was surprised to learn that vhost-scsi isn't widely used.
> > i thought vhost-scsi should be the favored solution since it should be 
> > faster but i guess the features you mentioned are also a significant factor.
> 
> Since virtio-scsi is QEMU userspace code it poses a lower security risk,
> is easier to update in sync with QEMU itself, and has all the QEMU block
> layer features.  The performance of vhost-scsi and virtio-scsi should be
> about the same - they both do the same thing and there's no great
> advantage to a kernel thread vs userspace thread (they use essentially
> the same functionality inside the kernel).
> 
> Stefan

That would depend on the workload.  I remember seeing reports of performance
differences, e.g.:

http://thread.gmane.org/gmane.comp.emulators.kvm.devel/93601/focus=93777

That was 4 years ago, it would be very interesting to see where we are now.

-- 
MST