Re: XENOPROF Problem

[Andrew Evans <andrewe@yahoo-inc.com>]

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Hi Ahmad,

I'm certainly not a Xenoprof expert, but I've learned a bit about it by
trial and error, with help from the xen-devel list. I've taken the
liberty of Cc:ing xen-devel so that others more knowledgeable than me
can help you. I haven't tried passive domains yet, and I'll say up front
that I don't know why Xenoprof isn't working for you with passive domains.

On 02/11/10 13:37, Ahmad Hassan wrote:
> Hi Andrew,
>
> I need help in using xenoprof. I installed the xenoprof on Dom0 and
> DomU as follows:
>
>     * Download Oprofile:
>       http://prdownloads.sourceforge.net/oprofile/oprofile-0.9.5.tar.gz
>     * Download XenoProf
>       patch: http://xenoprof.sourceforge.net/oprofile-0.9.5-xen.patch
>     * tar –zxvf oprofile-0.9.5.tar.gz
>     * cd oprofile-0.9.5
>     * patch –p1 < ../oprofile-0.9.5-xen-rc2.patch ./configure
>       –with-kernel-support
>     * make
>     * make install
>

That looks right to me. You also need Xenoprof support in your dom0
kernel. If you're using one of the kernels from the Xen source tree and
you can `modprobe oprofile` successfully, you should be ok.

> I am interested in measuring profiling overhead in XEN. So which kind
> of event should I capture.

You want to measure the overhead of the profiler itself? I guess you get
that "for free" -- time spent in oprofile kernel code should show up in
opreport in dom0, I think.

Which performance counter you use depends on what you're trying to
measure. If you just want to find out where CPU time is spent,
CPU_CLK_UNHALTED should do that for you. That's what I've been doing.

> Is it possible to capture all the events?

You can specify multiple events, though I haven't tried it. The opreport
web page talks about output for multiple events here:

http://oprofile.sourceforge.net/doc/opreport.html#opreport-comparison

I'd guess you'd just specify --event multiple times when you --start-daemon.

>   I followed the following passive profiling approach but I did not
> get any data.
>
> Dom0: opcontrol --reset
> Dom1: opcontrol --reset
> Dom0: opcontrol --start-daemon --event=
> CPU_IO_REQUESTS_TO_MEMORY_IO:1000000 --xen=/boot/xen-syms-3.4.1  
> --vmlinux=/boot/vmlinux  --passive-domains=1
> --passive-images=/boot/vmlinux
> *At the above command, I get the warning as :
> /dev/oprofile/passive-domains Permission Denied* but daemon starts
> eventually

This is a silly question, but you are running this as root, correct? If
you are running as root and getting this error, I think something is
wrong either in Xen or your dom0 kernel. `xm dmesg` may have error
messages that give clues -- check it before and after starting the daemon.

> Dom0: opcontrol --start
> AFTER 30 MINUTE
> Dom0: opcontrol –stop
> Dom0: opcontrol --dump
> Dom0: opcontrol –shutdown
>
> But when I try to "opreport -l" ti says that: "opreport error: No
> sample file found: try running opcontrol --dump or specfiy a session
> containing sample file"
>
>
> Can you please help me in that?
>
> Thanks.
>
> Best Regards, Hassan
> http://cern.ch/ahmadh/portfolio
>
> Erasmus Student
> The University of Reading, UK
> Aristotle University of Thessaloniki, Greece
> The University Of Carlos III, Madrid Spain
>
>


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