Messages in this thread | | | Date | Thu, 12 Feb 2015 11:28:14 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v5] perf: Use monotonic clock as a source for timestamps |
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On Thu, Feb 12, 2015 at 12:04:54PM +0200, Adrian Hunter wrote: > On 11/02/15 18:12, Peter Zijlstra wrote: > > > > 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.
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