Messages in this thread | | | Date | Fri, 8 May 2015 01:27:56 +0000 (UTC) | From | Mathieu Desnoyers <> | Subject | Re: [PATCH] ftrace: Provide trace clock monotonic raw |
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----- Original Message ----- > 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. > > What's the consensus on this patch? Everyone OK with it? If so, can you > please post a new patch with the proper change log. And can everyone > else give acks. I can take it in my tree.
I can see it being useful for tracing early boot, e.g. when debugging issues with NTP. So adding it to ftrace makes sense to me.
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Thanks,
Mathieu
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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