Re: Benchmarking for vhost polling patch

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, Nov 16, 2014 at 02:08:49PM +0200, Razya Ladelsky wrote:
> Razya Ladelsky/Haifa/IBM@IBMIL wrote on 29/10/2014 02:38:31 PM:
> 
> > From: Razya Ladelsky/Haifa/IBM@IBMIL
> > To: mst@redhat.com
> > Cc: Razya Ladelsky/Haifa/IBM@IBMIL, Alex Glikson/Haifa/IBM@IBMIL, 
> > Eran Raichstein/Haifa/IBM@IBMIL, Yossi Kuperman1/Haifa/IBM@IBMIL, 
> > Joel Nider/Haifa/IBM@IBMIL, abel.gordon@gmail.com, kvm@vger.kernel.org
> > Date: 29/10/2014 02:38 PM
> > Subject: Benchmarking for vhost polling patch
> > 
> > Hi Michael,
> > 
> > Following the polling patch thread: http://marc.info/?
> > l=kvm&m=140853271510179&w=2, 
> > I changed poll_stop_idle to be counted in micro seconds, and carried out 
> 
> > experiments using varying sizes of this value. 
> > 
> > If it makes sense to you, I will continue with the other changes 
> > requested for 
> > the patch.
> > 
> > Thank you,
> > Razya
> > 
> > 
> 
> Dear Michael,
> I'm still interested in hearing your opinion about these numbers 
> http://marc.info/?l=kvm&m=141458631532669&w=2, 
> and whether it is worthwhile to continue with the polling patch.
> Thank you,
> Razya 
> 
> 
> > 
> > 

Hi Razya,
On the netperf benchmark, it looks like polling=10 gives a modest but
measureable gain.  So from that perspective it might be worth it if it's
not too much code, though we'll need to spend more time checking the
macro effect - we barely moved the needle on the macro benchmark and
that is suspicious.
Is there a chance you are actually trading latency for throughput?
do you observe any effect on latency?
How about trying some other benchmark, e.g. NFS?


Also, I am wondering:

since vhost thread is polling in kernel anyway, shouldn't
we try and poll the host NIC?
that would likely reduce at least the latency significantly,
won't it?


-- 
MST