netdev - Re: Network performance with small packets

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Date:	Thu, 27 Jan 2011 12:15:05 -0800
From:	Shirley Ma <mashirle@...ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Steve Dobbelstein <steved@...ibm.com>, kvm@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: Network performance with small packets

On Thu, 2011-01-27 at 22:05 +0200, Michael S. Tsirkin wrote:
> Interesting. Could this is be a variant of the now famuous bufferbloat
> then?
> 
> I guess we could drop some packets if we see we are not keeping up.
> For
> example if we see that the ring is > X% full, we could quickly
> complete
> Y% without transmitting packets on. Or maybe we should drop some bytes
> not packets.
It's worth to try to figure out what's the best approach. I will make a
patch.


> > 
> > Requesting guest notification and extra interrupts is what we want
> to
> > avoid to reduce VM exits for saving CPUs. I don't think it's good.
> 
> Yes but how do you explain regression?
> One simple theory is that guest net stack became faster
> and so the host can't keep up.

Yes, that's what I think here. Some qdisc code has been changed
recently.

> > 
> > By polling the vq a bit more aggressively, you meant vhost, right?
> > 
> > Shirley
> 
> Yes. 

I had a similar patch before, I can modify it and test it out.

Shirley

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