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Re: [Xen-devel] [PATCH] Network Checksum Removal

On Monday 23 May 2005 03:13 pm, Keir Fraser wrote:
> On 23 May 2005, at 20:55, Bin Ren wrote:
> > I've added the support for ethtools. By turning on and off netfront
> > checksum offloading, I'm getting the following throughput numbers,
> > using iperf. Each test was run three times. CPU usages are quite
> > similar in two cases ('top' output). Looks like checksum computation
> > is not a major overhead in domU networking.
> >
> > dom0/1/2 all have 128M memory. dom0 has e1000 tx checksum offloading
> > turned on.
> What happens to CPU usage in dom1 when tx checksumming is disabled?
> Overall though these are the kind of results I would expect. Linux
> usually does csumming at the same time as it has to do a copy anyway,
> and it ends up being limited by memory/L2-cache bandwidth, not the
> extra computation. But the offload extensions haven't cost much to
> implement and there are probably cases where it helps a little.
> Maybe I'm being pessimistic though: Can you reproduce the rather more
> impressive speedups that you previously saw, Jon?

Alright, I broke down and got a BK puller.  

I get the following domU->dom0 throughput on my system (using netperf3 
TCP_STREAM testcase):
tx on   ~1580Mbps
tx off  ~1230Mbps

with my previous patch (on Friday's build), I was seeing the following:
with patch      ~1610Mbps
no patch                ~1100Mbps

The slight difference between the two might be caused by the changes that were 
incorporated in xen between those dates.  If you think it is worth the time, 
I can back port the latest patch to Friday's build to see if that makes a 


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