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Re: [Xen-devel] help with horrible network failures

To: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] help with horrible network failures
From: Nivedita Singhvi <niv@xxxxxxxxxx>
Date: Wed, 02 Mar 2005 10:01:14 -0800
Cc: Rob Gardner <rob.gardner@xxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxxx>, ian.pratt@xxxxxxxxxxxx
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Ian Pratt wrote:

I've got two machines running identical versions of xen & linux. One of them constantly has problems under high network loads (70-100% httperf loads). This is using xen-unstable checked out on or about Feb 13. Any clues? See below for details.

One machine exhibits the bug, the other doesn't? How similar is the h/w?

I believe this is a known unresolved bug in mainline.
It's possible Rob is provoking it by using NAPI - and
it is load-related, so that might explain why one box
is seeing it and one isn't. Essentially, data is getting
reordered where it really shouldn't, due to a race that
isn't clear. It would be very helpful to track this down
finally - if it hasn't already..

Can you reproduce with a single high-rate TCP stream? Do you have any of
the iptables/netfilter connection tracking stuff in your kernel?

Can you reproduce with an older version of Xen?

I suspect that it is independent of Xen - unless some versions
of Xen slow down traffic enough to change the window..


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