Re: [Xen-devel] profiling active RHEL 4 PV domains with xenoprof

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

It's been a long time since I played with oprofile; I think it could
use some serious attention, but it's been on my "list of important
things to do someday" for about 2 years now. :-)

Re the PV kernels: are you sure that the PV kernel has support for Xen
profiling? PV xenoprofile makes hypercalls to Xen to set up the
performance event counters.  But if that isn't set up properly, or for
some other reason doesn't work right, the guest oprofile may default
back to using only timers, for which it doesn't need Xen's help (but
which are less accurate especially in a virtual environment).

 -George

On Fri, Jan 29, 2010 at 1:37 AM, Andrew Evans <andrewe@xxxxxxxxxxxxx> wrote:
> Hi,
>
> Is it necessary to run a xenoprof-patched oprofile in a PV domU being
> actively profiled? I ask because
>
> http://xenoprof.sourceforge.net/xenoprof_2.0.txt
>
> seems to say no (no mention of --xen switch) but
>
> http://www.xen.org/files/summit_3/xenoprof_tutorial.pdf
>
> seems to say yes (specifies use of --xen in domUs). I'm running RHEL 4
> in the domU I want to actively profile, and RHEL 4 provides the ancient
> oprofile-0.8.1 package, with no support for the --xen switch. I've
> gotten oprofile 0.9.6 with xenoprof patches built on RHEL 4 but haven't
> been able to test it due to XENOPROF_start failing (see other message).
>
> Another thing I'm confused about: the above xenoprof tutorial also
> specifies use of the --event switch in domUs, saying they must use the
> same event as dom0. Makes sense, but my domUs are PV, and oprofile says
> only timer interrupts are usable. So must I also use timer interrupts on
> dom0?
>
> thanks,
>
> -Andrew
>
>
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