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Re: [Xen-devel] Poor performance on HVM (kernbench)

To: deshantm@xxxxxxxxx
Subject: Re: [Xen-devel] Poor performance on HVM (kernbench)
From: Steve Ofsthun <sofsthun@xxxxxxxxxxxxxxx>
Date: Wed, 10 Sep 2008 17:51:55 -0400
Cc: Daniel Magenheimer <dan.magenheimer@xxxxxxxxxx>, xen-devel mailing list <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Todd Deshane wrote:
On Wed, Sep 10, 2008 at 5:37 PM, Daniel Magenheimer
<dan.magenheimer@xxxxxxxxxx> wrote:
This doesn't answer the HVM question but it appears that
you are running guests with 1 vCPU but comparing against
a dual-CPU native.  True?

Yes. The intuition is that we don't want to overcommit virtual CPUs
since then you are stressing the schedulers more.

I think what Dan is getting at is, the native execution run should restrict it's cpu and memory usage to be 
identical with the guest tests.  So restrict the native test cpus with "maxcpus=1" or 
"nosmp" on the boot line.  Similarly you can restrict memory using "mem=xxxM".

I ran some tests with 2 vCPUs and all the numbers are a bit higher (as
having two CPUs tackling a compile is faster).

Although overcommit (of CPUs and memory ;) is interesting, we leave a
CPU dedicated to the host system (linux/dom0)
on purpose.


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