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    SubjectRe: [PATCH] ftrace: Provide trace clock monotonic raw
    ----- 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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