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[Xen-devel] Re: XENOPROF Problem

To: Ahmad Hassan <ahmad.hassan@xxxxxxxxx>
Subject: [Xen-devel] Re: XENOPROF Problem
From: Andrew Evans <andrewe@xxxxxxxxxxxxx>
Date: Thu, 11 Feb 2010 15:39:20 -0800
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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:


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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