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Re: [Xen-devel] CAP and performance problem

On gio, 2013-06-06 at 10:02 +0100, George Dunlap wrote:
> Well for one, from the scheduler's perspective, the promise isn't that 
> you'll get 50% of the *performance*, but 50% of the *cpu time*.  I 
> haven't been following the thread terribly closely, but I don't remember 
> seeing any xentop or xentrace reports.  
Yep, I suggested monitoring the vcpu usage, and Massimo reported a
correct 50% utilization for the vcpu in question in xentop.

> The first question is, other 
> than performance, do you have any reason to believe that the VM is not 
> getting 50% of the cpu time?
It correctly gets 50% for me, and for Massimo too, as per what he said
in one other e-mail in the thread.

I agree that it's vcpu utilization and non guest performance we're in
control of, but for a purely CPU bound workload, I guess one can expect
some sort of relationship between the two things, can't him? Besides,
that's right what I get in my tests with Massimo's code. :-)

> At some point while your test is running, could you execute the 
> following command in dom0:
> xentrace -D -e 0x21000 -T 10 /tmp/test.trace
> This will take a 10-second trace of just the scheduling events, placing 
> the result in /tmp/test.trace
> Then download and build xenalyze from the hg repo here:
> http://xenbits.xen.org/ext/xenalyze
> and run he following command:
> xenalyze -s /tmp/test.trace > /tmp/test.summary
> And post the results here?
Yes, I suggested trying to produce some traces too. However, having seen
that I get numbers consistent with the expectations, I now wonder what
can interact with the scheduler and make Massimo's results different...


<<This happens because I choose it to happen!>> (Raistlin Majere)
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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