Messages in this thread | | | Subject | Re: [RFC][PATCH 3/5] perf: Add hrtimer code for PMI-less hardware counters | From | Peter Zijlstra <> | Date | Mon, 30 Aug 2010 14:55:02 +0200 |
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On Mon, 2010-08-30 at 13:13 +0100, Matt Fleming wrote: > Currently, it's impossible to periodically sample hardware counters that > lack performance monitoring interrupt (PMI) support. In order to sample > these counters we can create an event group which is backed by a > hrtimer, thereby simulating a PMI. > > When the hrtimer goes off we sample the values in the hardware > counters. Because we obviously can't rely on the hrtimer going off at > exactly the sample period (say, every 1000 cache misses) the values need > to be weighted by the variable period since the last hrtimer went > off. This is so that we can compensate for the variability in hrtimer > period. > > If perf record tries to create a sampling counter and the hardware > doesn't support it then we'll fall back to creating an event group with > a hrtimer.
Why is this changing kernel code?
You can create those groups in userspace..
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