Re: perf_event self-monitoring overhead regression

[Vince Weaver]

On Thu, 1 Dec 2011, stephane eranian wrote:

> I take it your test is all about self-monitoring, single event, single thread.
> Did you try breaking down the cost using  TSC and rdtsc() to pinpoint where the
> regression is coming from in the 3 perf_event syscalls you're using?

I've started gathering results using rdtsc() and the results are even more 
puzzling.  

See:
   http://web.eecs.utk.edu/~vweaver1/projects/perf-events/benchmarks/rdtsc_overhead/core2_raw_null_kernel_rdtsc.png
for example.

Those results are from a core2 machine, with the CPU scaling governor set 
to "performance", the test bound to CPU0, and the test run 1000 times.

Part of the issue is that a few of those kernels are Debian unstable 
distro kernels and not hand-compiled stock kernels.  I'll rebuild a full 
set of kernels myself and see if I can reproduce the results.

Vince

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