netdev - Re: Network performance with small packets

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Message-ID: <20110201214211.GB31105@redhat.com>
Date:	Tue, 1 Feb 2011 23:42:11 +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 01:32:35PM -0800, Shirley Ma wrote:
> On Tue, 2011-02-01 at 23:24 +0200, Michael S. Tsirkin wrote:
> > My theory is that the issue is not signalling.
> > Rather, our queue fills up, then host handles
> > one packet and sends an interrupt, and we
> > immediately wake the queue. So the vq
> > once it gets full, stays full.
> 
> >From the printk debugging output, it might not be exactly the case. The
> ring gets full, run a bit, then gets full, then run a bit, then full...

Yes, but does it get even half empty in between?

> > If you try my patch with bufs threshold set to e.g.
> > half the vq, what we will do is send interrupt after we have processed
> > half the vq.  So host has half the vq to go, and guest has half the vq
> > to fill.
> > 
> > See?
> 
> I am cleaning up my set up to run your patch ...
> 
> Shirley
> 
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