Re: [PATCH v5] perf: Use monotonic clock as a source for timestamps
From: Peter Zijlstra <hidden>
Date: 2015-02-12 10:28:27
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- 2015-02-02 · Re: [PATCH v5] perf: Use monotonic clock as a source for timestamps · Pawel Moll <hidden>
- 2015-01-21 · [PATCH v5] perf: Use monotonic clock as a source for timestamps · Pawel Moll <hidden>
On Thu, Feb 12, 2015 at 12:04:54PM +0200, Adrian Hunter wrote:
On 11/02/15 18:12, Peter Zijlstra wrote:quoted
How about something like the below? I _think_ it should mostly work for x86, where the tsc is a 64bit wide cycle counter.It would have to be based on CLOCK_MONOTONIC_RAW not CLOCK_MONOTONIC
Why?
and you would have to check the clocksource is TSC.
It implicitly does that; it has that sched_clock_stable() thing, but yeah I suppose someone could change the clocksource even though the tsc is stable. Not using TSC when its available is quite crazy though.. but sure.
Why is CLOCK_MONOTONIC preferred anyway - I would have thought any adjustment would skew performance timings?
Because you can do inter-machine stuff with MONOTONIC and that's entirely impossible with MONO_RAW.