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SubjectRe: [PATCH 1/2] perf: Add sampling of the raw monotonic clock
On Thu, Sep 18, 2014 at 03:34:32PM +0100, Pawel Moll wrote:
> @@ -4456,6 +4459,13 @@ static void __perf_event_header__init_id(struct perf_event_header *header,
> data->cpu_entry.cpu = raw_smp_processor_id();
> data->cpu_entry.reserved = 0;
> }
> +
> + if (sample_type & PERF_SAMPLE_CLOCK_RAW_MONOTONIC) {
> + struct timespec now;
> +
> + getrawmonotonic(&now);
> + data->clock_raw_monotonic = timespec_to_ns(&now);
> + }
> }
>

This cannot work, getrawmonotonic() isn't NMI-safe and there's
nothing stopping this being used from NMI context.

Also getrawmonotonic() + timespec_to_ns() will make tglx sad, he's just
done a tree-wide eradication of silly conversions and now you're adding
a ns -> timespec -> ns dance right back.

I _think_ you want ktime_get_mono_fast_ns(), but this does bring us
right back to the question/discussion on which timebase you'd want to
sync again. MONO does make sense for most cases, but I think we've had
fairly sane stories for people wanting to sync against other clocks.

A well..


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