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Re: [Xen-devel] what's maximum speed setting for xen network?

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] what's maximum speed setting for xen network?
From: Nivedita Singhvi <nsnix@xxxxxxxxxxx>
Date: Sat, 23 Apr 2005 10:36:39 -0700
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, zhaoxin@xxxxxxxxxxxxxx, mukesh agrawal <lists.xensource.com@xxxxxxxxxxxxxxxxxxx>
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Keir Fraser wrote:

On 22 Apr 2005, at 20:53, mukesh agrawal wrote:

I've got a configuration with DomU talking to Dom0 over a vif, and seem to be seeing UDP losses, even at low data rates. (I haven't dug into this deeply to very the problem yet, though.) So I'd be interested if you're seeing something similar.


We have no back-pressure / flow control on inter-domain networking. This leads to embarrassing performance for UDP when the sender and receiver share a CPU. The sender fills the receiver's buffers but continues to send even though he drops further packets (no buffer space at receiver) -- then the receiver gets a time slice, receives a ring's worth of packets -- then the sender gets to run for another time slice, most of which again is wasted -- and so on.

We need a sensible mechanism for ensuring batched packet delivery, but also to ensure that comms rings do not so easily get overflowed. This would vastly improve the inter-domain performance, far more than striving for zero copy or other such tweaks.

It would be great if someone else is interested in investigating this. :-)

Hi Keir,

Yep, I'm one of the people at least looking into this, don't know
if others are too :). Thrown some instrumentation in and doing some
testing as we speak. Really needed some profiling so was trying to
get the oprofile stuff to work in unstable. From what I saw from
his last post, Jose is working on it.

A few people have kindly agreed to do some testing for me too.

We'll throw some stuff out on the list after the weekend.  I am
tracking all the reports of poor networking performance so if
people do see some issues please continue to post on the list..

thanks,
Nivedita


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