Re: [Xen-users] Xen Performance

Peter Booth
Sat, 30 May 2009 19:38:50 -0000

The original question doesn''t say "as measured on Dom0", and
appears
to reference the well known
study performed at Cambridge University and replicated at Clarkson
University. That study used a handful
of benchmarks and compared throughput across a number of
virtualization platforms. It found that, for those
tests, Xen throughput was, at most, only 8% worse than native Linux.

The issue for our community, however, is that it is human nature to
use the "at most 8% worse"
as a data-point for Xen performance.  But throughput is not the whole
picture. Many Xen installations
are hosting user-facing web applications where response time is much
more important than throughput.
Xen often increases the variability of response times.

One real world example:
native Linux:  		page response times of (  400ms/150ms) [mean/standard
deviation]
Xen VM:			page response times of (  700ms/3.5s) [mean/standard
deviation]

In this scenario, we have mean response times that are almost 100%
worse, and the 90th percentile is 1000% worse.

Peter Booth




On May 28, 2009, at 1:08 PM, Javier Guerra wrote:

> On Thu, May 28, 2009 at 11:57 AM, Peter Booth <peter_booth@mac.com>
> wrote:
>>
>> The 8% is a dangerous over-simplification, and represents simply
>> the results
>> of a particular well-designed study.
>>  Clearly there are situations where the overhead of using Xen is
>> much higher
>> than this.
>
> but not as measured on Dom0, as i think the original question was
>
> --
> Javier
>
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