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Date: Wed, 7 Dec 2011 16:44:19 -0800 From: stephane eranian <eranian@...glemail.com> To: Vince Weaver <vweaver1@...s.utk.edu> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Ingo Molnar <mingo@...e.hu>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Paul Mackerras <paulus@...ba.org>, Arnaldo Carvalho de Melo <acme@...stprotocols.net> Subject: Re: perf_event self-monitoring overhead regression On Tue, Dec 6, 2011 at 1:07 PM, Vince Weaver <vweaver1@...s.utk.edu> wrote: > 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. > Are those the results for surrounding the ioctl() with rdtsc()? What do the axis actually represent? > 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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