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SubjectRe: [PATCH 2/4] perf_event: add PERF_COUNT_HW_REF_CPU_CYCLES generic PMU event

* Stephane Eranian <eranian@google.com> wrote:

> This event counts the number of reference core cpu cycles.
> Reference means that the event increments at a constant rate
> which is not subject to core CPU frequency adjustments. The
> event may not count when the processor is in halted (low
> power) state. As such, it may not be equivalent to wall clock
> time. However, when the processor is not halted state, the
> event keeps a constant correlation with wall clock time.
>
> Signed-off-by: Stephane Eranian <eranian@google.com>
> ---
> include/linux/perf_event.h | 1 +
> 1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 564769c..0885561 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -54,6 +54,7 @@ enum perf_hw_id {
> PERF_COUNT_HW_BUS_CYCLES = 6,
> PERF_COUNT_HW_STALLED_CYCLES_FRONTEND = 7,
> PERF_COUNT_HW_STALLED_CYCLES_BACKEND = 8,
> + PERF_COUNT_HW_REF_CPU_CYCLES = 9,

Btw., that was what 'bus cycles' tried to do a long time ago:
the constant, non-variable baseline heartbeat of the system.

We could simply rename that, fix the event tables where needed,
and keep the ABI.

Just a small detail: how about naming it 'constant [frequency]
CPU cycles'? That's a concept that might be present on other
platforms as well.

CONST_FREQ_CYCLES or so. The 'CPU' can be dropped as well
because it's not really the CPU's frequency anymore.

Thanks,

Ingo


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