Date: Mon, 4 May 2015 22:57:48 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Drew Richardson <drew.richardson@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        John Stultz <john.stultz@linaro.org>,
        Wade Cherry <Wade.Cherry@arm.com>, Pawel Moll <pawel.moll@arm.com>
Subject: Re: [PATCH] ftrace: Provide trace clock monotonic raw
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On Mon, May 04, 2015 at 01:05:19PM -0700, Drew Richardson wrote:
> I'm collecting and merging data from perf, with Android Atrace data
> (writes to /sys/kernel/debug/tracing/trace_marker) which ends up in
> the ftrace stream and other measurements collected from
> userspace. Currently the only clock readable from userspace, supported
> by perf and by ftrace is CLOCK_MONOTONIC. However this clock is
> affected by the incremental adjustments performed by adjtime(3) and
> NTP. 

Which should not matter at all, right? If both sources are using the
same clock (they are) then its trivial to merge them and everything
works as expected.

> But I'd prefer to use a clock that is advancing at a consistent
> rate, hence CLOCK_MONOTONIC_RAW.

Right, Mathieu is asking _why_ you prefer that?
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