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

[Jeff Sturm <jeff.sturm@xxxxxxxxxx>]

> -----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.

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).

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.

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

Jeff



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