netdev - Re: Network performance with small packets

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Date:	Wed, 2 Feb 2011 20:20:25 +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 Wed, Feb 02, 2011 at 07:42:51AM -0800, Shirley Ma wrote:
> On Wed, 2011-02-02 at 12:49 +0200, Michael S. Tsirkin wrote:
> > On Tue, Feb 01, 2011 at 11:33:49PM -0800, Shirley Ma wrote:
> > > On Tue, 2011-02-01 at 23:14 -0800, Shirley Ma wrote:
> > > > 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. 
> > > 
> > > I meant w/o guest change, only vhost changes. Sorry about that.
> > > 
> > > Shirley
> > 
> > Ah, excellent. What were the parameters? 
> 
> I used half of the ring size 129 for packet counters,
> but the
> performance is still not as good as dropping packets on guest, 3.7 Gb/s
> vs. 6.2Gb/s.
> 
> Shirley

How many packets and bytes per interrupt are sent?
Also, what about other values for the counters and other counters?

What does your patch do? Just drop packets instead of
stopping the interface?

To have an understanding when should we drop packets
in the guest, we need to know *why* does it help.
Otherwise, how do we know it will work for others?
Note that qdisc will drop packets when it overruns -
so what is different? Also, are we over-running some other queue
somewhere?

-- 
MST
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