netdev - Re: [v2 RFC PATCH 0/4] Implement multiqueue virtio-net

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Message-ID: <20101014081723.GC11095@redhat.com>
Date:	Thu, 14 Oct 2010 10:17:23 +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, kvm@...r.kernel.org, netdev@...r.kernel.org,
	rusty@...tcorp.com.au
Subject: Re: [v2 RFC PATCH 0/4] Implement multiqueue virtio-net

On Thu, Oct 14, 2010 at 01:28:58PM +0530, Krishna Kumar2 wrote:
> "Michael S. Tsirkin" <mst@...hat.com> wrote on 10/12/2010 10:39:07 PM:
> 
> > > Sorry for the delay, I was sick last couple of days. The results
> > > with your patch are (%'s over original code):
> > >
> > > Code               BW%       CPU%       RemoteCPU
> > > MQ     (#txq=16)   31.4%     38.42%     6.41%
> > > MQ+MST (#txq=16)   28.3%     18.9%      -10.77%
> > >
> > > The patch helps CPU utilization but didn't help single stream
> > > drop.
> > >
> > > Thanks,
> >
> > What other shared TX/RX locks are there?  In your setup, is the same
> > macvtap socket structure used for RX and TX?  If yes this will create
> > cacheline bounces as sk_wmem_alloc/sk_rmem_alloc share a cache line,
> > there might also be contention on the lock in sk_sleep waitqueue.
> > Anything else?
> 
> The patch is not introducing any locking (both vhost and virtio-net).
> The single stream drop is due to different vhost threads handling the
> RX/TX traffic.
> 
> I added a heuristic (fuzzy) to determine if more than one flow
> is being used on the device, and if not, use vhost[0] for both
> tx and rx (vhost_poll_queue figures this out before waking up
> the suitable vhost thread).  Testing shows that single stream
> performance is as good as the original code.

...

> This approach works nicely for both single and multiple stream.
> Does this look good?
> 
> Thanks,
> 
> - KK

Yes, but I guess it depends on the heuristic :) What's the logic?

-- 
MST
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