linux-kernel - Re: [tip:perf/timer] perf: Add per event clockid support

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Message-ID: <CABPqkBT085NLB1qVPy26E7PUcVTyb507nF5fBksJiFEKk69P-A@mail.gmail.com>
Date:	Fri, 27 Mar 2015 10:00:00 -0700
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	John Stultz <john.stultz@...aro.org>,
	"H. Peter Anvin" <hpa@...or.com>, David Ahern <dsahern@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [tip:perf/timer] perf: Add per event clockid support

On Fri, Mar 27, 2015 at 9:57 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, Mar 27, 2015 at 09:52:25AM -0700, Stephane Eranian wrote:
>> Ok, I see. But on architectures which do not have NMI, they would all
>> be safe. And that would work if they set the PERF_PMU_CAP_NO_NMI flag
>> on their pmu->capabilities.
>
> Indeed so. I have not audited them all as the current 'default' is safe.
>
>> Next, I am trying to understand how perf is going to expose this. I am
>> thinking about this in the context of my jitted code patches.
>
> I send you some preliminary patches for this.
>
>> With this approach, the jit runtime and the perf tool need to agree on
>> the clock they are using. That mean they need to advertise or document
>> the clock they use
>
> This is indeed still missing, I put an XXX question in one of the
> emails to this effect. I suppose we should store the used clockid in the
> data file. I just haven't figured out how all that code works.
>
>> and there needs to be an option in perf record to pass that same
>> clockid.
>
> I did indeed post a patch to do that.

I will switch my jitted patches to your approach to verify that this
actually works.
Thanks.
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