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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

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?
 -- Keir


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