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Subject: Re: [RFC] perf: need to expose sched_clock to correlate user
 samples with kernel samples
From: Steven Rostedt <rostedt@goodmis.org>
To: John Stultz <john.stultz@linaro.org>
Cc: Stephane Eranian <eranian@google.com>, Pawel Moll <pawel.moll@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
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        Paul Mackerras <paulus@samba.org>, Anton Blanchard <anton@samba.org>,
        Will Deacon <Will.Deacon@arm.com>,
        "ak@linux.intel.com" <ak@linux.intel.com>,
        Pekka Enberg <penberg@gmail.com>,
        Robert Richter <robert.richter@amd.com>, tglx <tglx@linutronix.de>
Date: Tue, 05 Feb 2013 20:19:55 -0500
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On Tue, 2013-02-05 at 14:28 -0800, John Stultz wrote:
> I prefer the ioctl method, since its less likely to be re-purposed/misused.
> 
> Though I'd be most comfortable with finding some way for perf-timestamps 
> to be CLOCK_MONOTONIC based (or maybe CLOCK_MONOTONIC_RAW if it would be 
> easier), and just avoid all together adding another time domain that 
> doesn't really have clear definition (other then "what perf uses").

Perhaps add a new perf system call? Does everything need to go through
the one great mighty perf_ioctl aka sys_perf_event_open()? I mean, if
there's something that can be agnostic to an event, but still very much
related to perf, perhaps another perf syscall should be created.

If people are worried about adding a bunch of new perf syscalls, maybe
add a sys_perf_control() system call that works like an ioctl but
without a file descriptor. Something for things that don't require an
event attached to it, like to retrieve a time stamp counter that perf
uses, but done in a way that it could be used for other things perf
related that does not require an event.

-- Steve