On Fri, May 08, 2015 at 03:09:03PM +0100, Steven Rostedt wrote: > 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 >
Sorry about that, thanks for your patience. -- 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/
