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Re: [Xen-devel] n/w performance degradation

To: Diwaker Gupta <diwaker.lists@xxxxxxxxx>
Subject: Re: [Xen-devel] n/w performance degradation
From: Nivedita Singhvi <niv@xxxxxxxxxx>
Date: Mon, 05 Dec 2005 16:09:43 -0800
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Diwaker Gupta wrote:

Hi folks,

I was to post this over the weekend, but didn't get around to it, and
look in the meanwhile Xen 3.0.0 was released! Good work all around,
but I got some performance problems to report :)

I'm running Changeset 00c349d5b40d269da4fec9510f1dd7c6bb3b3327. This
is a dual CPU machine but I'm currently running with noht, nosmp. All
tests are done using iperf -- both endpoints are sitting on the same
switch on our cluster. The machines have Broadcom BCM5704 NICs.

N/W performance from dom0 seems fine (though I used to get 930+ until
a few days back):

[  6]  0.0-20.0 sec  1.95 GBytes    835 Mbits/sec

However, from a VM, the throughput is really bad:

[  5]  0.0-20.0 sec  1.05 GBytes    450 Mbits/sec

The above numbers are using the BVT scheduler. With the SEDF
scheduler, the numbers are even worse (a VM can't get more than
300Mbps in my tests). I can post concrete figures if people are
interested. I'm _not_ running pipelined netback.

Is anyone else observing such performance problems?

Diwaker,

Can you run oprofile and obtain any kind of breakdown
on that, if possible? Also, are you dedicating individual
CPUs to dom0 and guest? (Avoiding much of the context
switching on I/O). What are your memory allocations? How much
of a bump do you get if you increase memory?

thanks,
Nivedita



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