On Tue, 5 May 2015 07:54:46 -0700 Drew Richardson <drew.richard...@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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
