Re: [PATCH 0/2] perf/x86: Add ability to sample TSC

From: John Stultz
Date: Thu Feb 19 2015 - 12:24:21 EST

On Thu, Feb 19, 2015 at 4:11 AM, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
> Hi
> With the advent of switching perf_clock to CLOCK_MONOTONIC,
> it will not be possible to convert perf_clock directly to/from
> TSC. So add the ability to sample TSC instead.
> Adrian Hunter (2):
> perf: Sample additional clock value
> perf/x86: Provide TSC for PERF_SAMPLE_CLOCK_ARCH

This doesn't seem very portable. The CLOCK_MONOTONIC_RAW clockid was
added to provide a arch-neutral abstraction of a free-running hardware
counter that isn't affected by adjtimex slewing (though like any
counter, it will be affected by non-constant drift).

You might consider looking at that if the short term slew adjustments
(which result in more accurate timings in the long term) are
problematic for you.

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