Re: [Xen-users] Linux DomU vs Bare Metal performance issues

[Mark Watts <m.watts@xxxxxxxxxxxxxxxxx>]

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On 03/12/2010 22:18, Jeff Sturm wrote:
>> -----Original Message-----
>> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-
>> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Mark Watts
>> Sent: Friday, December 03, 2010 2:40 PM
>> To: xen-users@xxxxxxxxxxxxxxxxxxx
>> Subject: [Xen-users] Linux DomU vs Bare Metal performance issues
>>
>> Can anyone shed any light on why I see such a drop in performance
> between these
>> two servers? I could understand, to an extent, seeing the DomU getting
> 3/4 of the
>> performance of the bare metal server given it has one CPU less, but
> this is less than
>> 1/2 the performance.
> 
> Understand what you're really testing here is the performance of the
> virtual network driver, since Apache does almost no work to serve a
> simple static page.  You're exercising the TCP stack and network drivers
> more than anything else.

Sure, but iperf shows near-enough line speed in both directions.
Shouldn't this 'prove' the virtual network driver is up to scratch for
this system?

> Out of curiosity, can you easily run the same test against dom0?  The
> dom0 runs a Xen kernel, on top of the hypervisor, but with a physical
> network interface (rather than virtual).

I can, certainly.

> One thing you can try is to pin the dom0 and/or domU to a physical core,
> using "xm vcpu-pin".  That gave me better throughput on some of my
> tests.

Dom-0 is already pinned to one CPU with the Dom-U given the remaining three.

> (I have doubts that hyperthreading scales as well as multicore
> processors, however I don't have any hyperthreaded systems of my own to
> test.)

I can certainly try this again with HT switched off on both boxes,
although that'll have to wait 'till monday.

Mark.



- -- 
Mark Watts, BSc RHCE
http://www.linux-corner.info/
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