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

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, <bin.ren@xxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH] Network Checksum Removal
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Mon, 23 May 2005 21:22:38 +0100
Cc: Andrew Theurer <habanero@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Jon Mason <jdmason@xxxxxxxxxx>
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Thread-index: AcVf1Fi+ZRLvoGrUTOKMabA4ykE+NgAAEing
Thread-topic: [Xen-devel] [PATCH] Network Checksum Removal
> 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?

We should be getting some benefit on the receive path, where the
checksum is normally forced to happen independent of a copy. Having this
offloaded to hardware should produce some measureable gain.

Bin: The numbers you're seeing are terrible anyway. You should be seeing
890Mb/s for external traffic. What kind of machine is this on?

Ian

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