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

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Date:	Thu, 28 Oct 2010 07:50:54 +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 10:44:14AM +0530, Krishna Kumar2 wrote:
> "Michael S. Tsirkin" <mst@...hat.com> wrote on 10/26/2010 04:39:13 PM:
> 
> (merging two posts into one)
> 
> > I think we discussed the need for external to guest testing
> > over 10G. For large messages we should not see any change
> > but you should be able to get better numbers for small messages
> > assuming a MQ NIC card.
> 
> For external host, there is a contention among different
> queues (vhosts) when packets are processed in tun/bridge,
> unless I implement MQ TX for macvtap (tun/bridge?).  So
> my testing shows a small improvement (1 to 1.5% average)
> in BW and a rise in SD (between 10-15%).  For remote host,
> I think tun/macvtap needs MQ TX support?

Confused. I thought this *is* with a multiqueue tun/macvtap?
bridge does not do any queueing AFAIK ...
I think we need to fix the contention. With migration what was guest to
host a minute ago might become guest to external now ...

> > > > > 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.
> 
> Thanks,
> 
> - KK
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