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

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Message-ID: <20101028061832.GA7590@redhat.com>
Date:	Thu, 28 Oct 2010 08:18:32 +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, netdev-owner@...r.kernel.org,
	rusty@...tcorp.com.au
Subject: Re: [v3 RFC PATCH 0/4] Implement multiqueue virtio-net

On Thu, Oct 28, 2010 at 11:42:05AM +0530, Krishna Kumar2 wrote:
> > "Michael S. Tsirkin" <mst@...hat.com>
> 
> > > > 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 ...
> 
> Macvtap RX is MQ but not TX. I don't think MQ TX support is
> required for macvtap, though. Is it enough for existing
> macvtap sendmsg to work, since it calls dev_queue_xmit
> which selects the txq for the outgoing device?
> 
> Thanks,
> 
> - KK

I think there would be an issue with using a single poll notifier and
contention on send buffer atomic variable.
Is tun different than macvtap? We need to support both long term ...

-- 
MST
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