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RE: [Xen-devel] Performance Counter Virtualization in Xen

To: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx>, "Santos, Jose Renato G" <joserenato.santos@xxxxxx>
Subject: RE: [Xen-devel] Performance Counter Virtualization in Xen
From: "Bhatia, Nikhil" <bhatia@xxxxxxxx>
Date: Mon, 21 May 2007 02:52:19 -0400
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, xen-users@xxxxxxxxxxxxxxxxxxx, xen-ppc-devel@xxxxxxxxxxxxxxxxxxx
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Thread-topic: [Xen-devel] Performance Counter Virtualization in Xen
Hi Christian,

Does the power PC still use the PM API for getting performance counters? I 
think, PAPI uses PMAPI underneath to get the performance counter data on a 
power PC. So, if there is a patched PMAPI library available for the Xen port on 
power PC, then a user might be able to easily use PAPI for per-domain 
profiling. Currently, I don't have an access to a Power PC machine with root 
privileges. However, if I get hold of such a machine, I would love to try this 
out and share my findings. 


-----Original Message-----
From: Christian Ehrhardt [mailto:ehrhardt@xxxxxxxxxxxxxxxxxx] 
Sent: Monday, May 21, 2007 2:37 AM
To: Santos, Jose Renato G
Cc: Bhatia, Nikhil; xen-users@xxxxxxxxxxxxxxxxxxx; 
xen-devel@xxxxxxxxxxxxxxxxxxx; xen-ppc-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] Performance Counter Virtualization in Xen

Well it's not "x86 architectures", but the current profiling support in 
xen on powerpc allows the use of performance counters from the domains 
as used from non-virtualized environments.
It is currently only tested with oprofile and has to be considered 
experimental because there are some known issues, but depending on your 
needs this might work for you.
As far as I read on 
http://icl.cs.utk.edu/papi/custom/index.html?lid=62&slid=96 PAPI has 
PPC970 support.
I do not know PAPI in detail, but it is possible that you can run it 
with less/no patching xen/linux on the current xenppc head.

Santos, Jose Renato G wrote:
> You are right,  currently the only available tool for using hardware 
> performance counters in Xen is XenOprofile. To expose a more generic 
> API to guests such as Perfmon, we would need to virtualize performance 
> counters. One of the challenges of virtualizing performance counters 
> is the high cost of saving and restoring perf. counters on domain 
> context switches. It may be possible to do some optimizations such as 
>  lazy save/restore that could help. Also it is expected that the cost 
> for accessing performance counters is going to be better in new 
> processors that are coming out from Intel and AMD. afaik, no one is 
> actively working on virtualizing HW performance counters in Xen.
> For other software metrics such as number of I/O operations you can 
> try Xenmon which report values of Xen performance counters (i.e SW 
> counters).
> Regards
> Renato
>     ------------------------------------------------------------------------
>     *From:* xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
>     [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] *On Behalf Of
>     *Bhatia, Nikhil
>     *Sent:* Friday, May 18, 2007 12:15 PM
>     *To:* xen-users@xxxxxxxxxxxxxxxxxxx
>     *Cc:* xen-devel@xxxxxxxxxxxxxxxxxxx
>     *Subject:* [Xen-devel] Performance Counter Virtualization in Xen
>     Hello Xenthusiasts,
>     I have a few questions regarding the performance monitoring of
>     applications and domains running on the latest version of Xen VMM
>     via the performance monitoring counters available in x86
>     architectures.
>     -          I have used Xenoprof by patching Xen-3.0.2 Xenolinux
>     and the Oprofile layer which enabled me to collect performance
>     counter values per domain (for a passive domain) and per
>     application (for an active domain). I was able to perform the
>     profiling via command line interface using Opcontrol and then
>     reporting the counters using Opreport. However, I was unable to
>     find a way to profile an application (using an API like PAPI)
>     because the perfctr port was not available for Xen. Is there a way
>     through which applications can be monitored using performance
>     counters?
>     -          Is there a Xen tool/utility which provides meaningful
>     information about per-domain metrics for dynamic memory usage
>     (e.g. reserved memory by Xen, total heap size in use, swap space
>     reserved per domain etc.), I/O done to/from the disc and the bytes
>     sent/received from the network over fixed intervals of time?
>     Thanks,
>     Best Regards,
>     Nikhil
> ------------------------------------------------------------------------
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Grüsse / regards, 
Christian Ehrhardt

IBM Linux Technology Center, Open Virtualization
+49 7031/16-3385

IBM Deutschland Entwicklung GmbH
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