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Date: Wed, 2 Feb 2011 12:48:43 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Shirley Ma <mashirle@...ibm.com>
Cc: Sridhar Samudrala <sri@...ibm.com>,
Steve Dobbelstein <steved@...ibm.com>,
David Miller <davem@...emloft.net>, kvm@...r.kernel.org,
mashirle@...ux.vnet.ibm.com, netdev@...r.kernel.org
Subject: Re: Network performance with small packets
On Tue, Feb 01, 2011 at 11:14:51PM -0800, Shirley Ma wrote:
> On Wed, 2011-02-02 at 08:29 +0200, Michael S. Tsirkin wrote:
> > On Tue, Feb 01, 2011 at 10:19:09PM -0800, Shirley Ma wrote:
> > > On Tue, 2011-02-01 at 22:05 -0800, Shirley Ma wrote:
> > > >
> > > > The way I am changing is only when netif queue has stopped, then
> > we
> > > > start to count num_free descriptors to send the signal to wake
> > netif
> > > > queue.
> > >
> > > I forgot to mention, the code change I am making is in guest kernel,
> > in
> > > xmit call back only wake up the queue when it's stopped && num_free
> > >=
> > > 1/2 *vq->num, I add a new API in virtio_ring.
> >
> > Interesting. Yes, I agree an API extension would be helpful. However,
> > wouldn't just the signaling reduction be enough, without guest
> > changes?
>
> w/i guest change, I played around the parameters,for example: I could
> get 3.7Gb/s with 42% CPU BW increasing from 2.5Gb/s for 1K message size,
> w/i dropping packet, I was able to get up to 6.2Gb/s with similar CPU
> usage.
We need to consider them separately IMO. What's the best we can get
without guest change? And which parameters give it?
There will always be old guests, and as far as I can tell
it should work better from host.
> > > However vhost signaling reduction is needed as well. The patch I
> > > submitted a while ago showed both CPUs and BW improvement.
> > >
> > > Thanks
> > > Shirley
> >
> > Which patch was that?
>
> The patch was called "vhost: TX used buffer guest signal accumulation".
Yes, a somewhat similar idea.
> You suggested to split add_used_bufs and signal.
Exactly. And this is basically what this patch does.
> I am still thinking
> what's the best approach to cooperate guest (virtio_kick) and
> vhost(handle_tx), vhost(signaling) and guest (xmit callback) to reduce
> the overheads, so I haven't submit the new patch yet.
>
> Thanks
> Shirley
--
MST
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