netdev - Re: [v3 RFC PATCH 0/4] Implement multiqueue virtio-net

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Message-ID: <20101029112603.GA24577@redhat.com>
Date:	Fri, 29 Oct 2010 13:26:03 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Krishna Kumar2 <krkumar2@...ibm.com>
Cc:	anthony@...emonkey.ws, arnd@...db.de, avi@...hat.com,
	davem@...emloft.net, eric.dumazet@...il.com, kvm@...r.kernel.org,
	netdev@...r.kernel.org, rusty@...tcorp.com.au
Subject: Re: [v3 RFC PATCH 0/4] Implement multiqueue virtio-net

On Thu, Oct 28, 2010 at 12:48:57PM +0530, Krishna Kumar2 wrote:
> > Krishna Kumar2/India/IBM wrote on 10/28/2010 10:44:14 AM:
> >
> > > > > > Results for UDP BW tests (unidirectional, sum across
> > > > > > 3 iterations, each iteration of 45 seconds, default
> > > > > > netperf, vhosts bound to cpus 0-3; no other tuning):
> > > > >
> > > > > Is binding vhost threads to CPUs really required?
> > > > > What happens if we let the scheduler do its job?
> > > >
> > > > Nothing drastic, I remember BW% and SD% both improved a
> > > > bit as a result of binding.
> > >
> > > If there's a significant improvement this would mean that
> > > we need to rethink the vhost-net interaction with the scheduler.
> >
> > I will get a test run with and without binding and post the
> > results later today.
> 
> Correction: The result with binding is is much better for
> SD/CPU compared to without-binding:

Can you pls ty finding out why that is?  Is some thread bouncing between
CPUs?  Does a wrong numa node get picked up?
In practice users are very unlikely to pin threads to CPUs.

-- 
MST
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