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

To: Mark Watts <m.watts@xxxxxxxxxxxxxxxxx>, <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-users] Linux DomU vs Bare Metal performance issues
From: Jeff Sturm <jeff.sturm@xxxxxxxxxx>
Date: Mon, 6 Dec 2010 23:57:22 -0500
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Thread-topic: [Xen-users] Linux DomU vs Bare Metal performance issues
> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-
> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Mark Watts
> Sent: Sunday, December 05, 2010 6:26 PM
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] Linux DomU vs Bare Metal performance issues
> > I can certainly try this again with HT switched off on both boxes,
> > although that'll have to wait 'till monday.
> Some updates:
> Running the same ab test against the Dom-0 gets me around 4,400 req/sec
> - - a modest increase over the Dom-U (~3,800).
> Rebooting my Dom-0 system into the standard CentOS 5.5 kernel sees the same
> 10,200 req/sec, so its clearly something related to this kernel which causes 
> the slow
> down.

Now, that's interesting-- my first guess would've been the net drivers, but 
since dom0 has a hardware NIC and exhibits similar performance, it sounds like 
we can rule that out.

There are many differences in the CentOS standard kernel configs vs. the dom0 
configs.  For instance, the dom0 kernel undefines CONFIG_X86_HT and lowers 
CONFIG_HZ to 250.  I don't know which of these settings, or the hypervisor for 
that matter, contributes the most to the performance drop you observe--I'd 
honestly be guessing.


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