Messages in this thread | | | From | Namhyung Kim <> | Subject | Re: [PATCH v2 1/2] perf tools: Add support for pinned modifier | Date | Wed, 07 Aug 2013 15:18:06 +0900 |
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Hi Michael,
On Tue, 6 Aug 2013 23:28:05 +1000, Michael Ellerman wrote: > This commit adds support for a new modifier "D", which requests that the > event, or group of events, be pinned to the PMU. > > The "p" modifier is already taken for precise, and "P" may be used in > future to mean "fully precise". > > So we use "D", which stands for pinneD - and looks like a padlock, or if > you're using the ":D" syntax perf smiles at you. > > This is an oft-requested feature from our HW folks, who want to be able > to run a large number of events, but also want 100% accurate results for > instructions per cycle. > > Comparison of results with and without pinning: > > $ perf stat -e '{cycles,instructions}:D' -e cycles,instructions,... > > 79,590,480,683 cycles # 0.000 GHz > 166,123,716,524 instructions # 2.09 insns per cycle > # 0.11 stalled cycles per insn > > 79,352,134,463 cycles # 0.000 GHz [11.11%] > 165,178,301,818 instructions # 2.08 insns per cycle > # 0.11 stalled cycles per insn [11.13%] > > As you can see although perf does a very good job of scaling the values > in the non-pinned case, there is some small discrepancy. > > The patch is fairly straight forward, the one detail is that we need to > make sure we only request pinning for the group leader when we have a > group.
Acked-by: Namhyung Kim <namhyung@kernel.org>
Thanks, Namhyung
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