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Re: [Xen-devel] Poor HVM performance with 8 vcpus

  • To: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
  • From: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
  • Date: Wed, 14 Oct 2009 11:17:07 +0200
  • Cc: Gianluca Guida <Gianluca.Guida@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Wed, 14 Oct 2009 02:17:35 -0700
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  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

Tim Deegan wrote:
> At 09:16 +0100 on 14 Oct (1255511785), Juergen Gross wrote:
>> as the performance of BS2000 seems to be hit by OOS optimization, I'm
>> thinking of making a patch to disable this feature by a domain parameter.
>> Is there a way to do this without having to change all places where the
>> #if statements are placed?
>> I think there should be some central routines where adding an "if" could
>> be enough (setting oos_active to 0 seems not to be enough, I fear).
>> Do you have any hint?
> The simplest way is to cause sh_unsync() to immediately return 0.  That
> won't be quite as fast as #defining it all away but will avoid the
> expensive paths that cause lock contention.  You can add your flag to
> the big if statement that's already there to avoid unsafe cases.

Thanks, I'll try.

> Incidentally, although your benchmark does poorly on 8 VCPUs it might be
> worth trying a less aggressively targeted benchmark -- we found on
> Windows VMs that more realistic tests (e.g. Sysmark) still showed a
> slight improvement from the OOS optimization at 8 vcpus.

The benchmark is designed to be a realistic simulation of a typical customer
batch load. Many BS2000 customers would see similar performance effects.


Juergen Gross                 Principal Developer Operating Systems
TSP ES&S SWE OS6                       Telephone: +49 (0) 89 636 47950
Fujitsu Technolgy Solutions               e-mail: juergen.gross@xxxxxxxxxxxxxx
Otto-Hahn-Ring 6                        Internet: ts.fujitsu.com
D-81739 Muenchen                 Company details: ts.fujitsu.com/imprint.html

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