netdev - Re: Network performance with small packets

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Message-ID: <1296748680.25430.169.camel@localhost.localdomain>
Date:	Thu, 03 Feb 2011 07:58:00 -0800
From:	Shirley Ma <mashirle@...ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Krishna Kumar2 <krkumar2@...ibm.com>,
	David Miller <davem@...emloft.net>, kvm@...r.kernel.org,
	mashirle@...ux.vnet.ibm.com, netdev@...r.kernel.org,
	netdev-owner@...r.kernel.org, Sridhar Samudrala <sri@...ibm.com>,
	Steve Dobbelstein <steved@...ibm.com>
Subject: Re: Network performance with small packets

On Thu, 2011-02-03 at 08:13 +0200, Michael S. Tsirkin wrote:
> > Initial TCP_STREAM performance results I got for guest to local
> host 
> > 4.2Gb/s for 1K message size, (vs. 2.5Gb/s)
> > 6.2Gb/s for 2K message size, and (vs. 3.8Gb/s)
> > 9.8Gb/s for 4K message size. (vs.5.xGb/s)
> 
> What is the average packet size, # bytes per ack, and the # of
> interrupts
> per packet? It could be that just slowing down trahsmission
> makes GSO work better. 

There is no TX interrupts with dropping packet.

GSO/TSO is the key for small message performance, w/o GSO/TSO, the
performance is limited to about 2Gb/s no matter how big the message size
it is. I think any work we try here will increase large packet size
rate. BTW for dropping packet, TCP increased fast retrans, not slow
start. 

I will collect tcpdump, netstart before and after data to compare packet
size/rate w/o w/i the patch.

Thanks
Shirley

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