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perf: Reimplement frequency driven sampling

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There was a bug in the old period code that caused intel_pmu_enable_all()
or native_write_msr_safe() to show up quite high in the profiles.

In staring at that code it made my head hurt, so I rewrote it in a
hopefully simpler fashion. Its now fully symetric between tick and
overflow driven adjustments and uses less data to boot.

The only complication is that it basically wants to do a u128 division.
The code approximates that in a rather simple truncate until it fits
fashion, taking care to balance the terms while truncating.

This version does not generate that sampling artefact.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra
2010-01-26 18:50:16 +01:00
committed by Ingo Molnar
parent ef12a14130
commit abd5071394
2 changed files with 94 additions and 43 deletions
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5
include/linux/perf_event.h
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@ -498,9 +498,8 @@ struct hw_perf_event {
atomic64_t period_left;
u64 interrupts;
u64 freq_count;
u64 freq_interrupts;
u64 freq_stamp;
u64 freq_time_stamp;
u64 freq_count_stamp;
#endif
};