Messages in this thread | | | Date | Fri, 8 May 2015 10:09:03 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] ftrace: Provide trace clock monotonic raw |
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On Tue, 5 May 2015 07:54:46 -0700 Drew Richardson <drew.richardson@arm.com> wrote:
> CLOCK_MONOTONIC_RAW will advance more constantly than CLOCK_MONOTONIC. > > Imagine someone is trying to optimize a particular program to reduce > instructions executed for a given workload while minimizing the effect > on runtime. Also suppose that ntp is running and potentially making > larger adjustments to CLOCK_MONOTONIC. If ntp is adjusting > CLOCK_MONOTONIC to advance more rapidly, the program will appear to > use fewer instructions per second but run longer than it would if > CLOCK_MONOTONIC_RAW had been used. The total number of instructions > observed would be the same regardless of the clock source used, but > how it's attributed to time would be affected. > > Conversely if ntp is adjusting CLOCK_MONOTONIC to advance more slowly, > the program will appear to use more instructions per second but run > more quickly. Of course there are many sources that can cause jitter > in performance measurements on modern processors, but I'd like to > remove ntp from the list.
This is a nice description, and was expecting to see it in the change log of the latest patch. Can you resend with a more detailed description (like the above).
Thanks!
-- Steve
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