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Re: [Xen-users] CPU intensive VM starves IO intensive VMs

To: "Tim Wood" <twwood@xxxxxxxxx>
Subject: Re: [Xen-users] CPU intensive VM starves IO intensive VMs
From: "Diwaker Gupta" <diwaker.lists@xxxxxxxxx>
Date: Fri, 1 Sep 2006 17:00:04 -0700
Cc: "Apparao, Padmashree K" <padmashree.k.apparao@xxxxxxxxx>, Xen Users <xen-users@xxxxxxxxxxxxxxxxxxx>
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On 8/30/06, Tim Wood <twwood@xxxxxxxxx> wrote:
> On 8/29/06, Apparao, Padmashree K <padmashree.k.apparao@xxxxxxxxx> wrote:
> What are the number of vcpus so for each VM and what physical cpus are
> the VMs on.  I have run similar tests and seen different results from
> what you see.

For these experiments I am working on a single CPU machine. Having
more cpus would be nice, but I'm assuming setting the sedf CPU weights
should be sufficient for preventing any VM or Dom0 from being starved.

Single CPU machines are typically bad for such experiments. In Xen,
the execution of any I/O intensive domain gets coupled with the
execution of Domain-0 (since any traffic necessarily needs to go
through Domain-0 first). This coupling makes scheduling inefficient,
affecting the performance.

If you have a single processor P4, try enabling HT and putting Dom-0
on a thread by itself. If you can get your hands on an SMP, that would
be the best.

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