Message-ID: <515C393C.8030405@gmail.com>
Date: Wed, 03 Apr 2013 08:14:20 -0600
From: David Ahern <dsahern@gmail.com>
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To: Stephane Eranian <eranian@google.com>
CC: John Stultz <john.stultz@linaro.org>, Pawel Moll <pawel.moll@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, "mingo@elte.hu" <mingo@elte.hu>,
        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>, Steven Rostedt <rostedt@goodmis.org>,
        Robert Richter <robert.richter@amd.com>
Subject: Re: [RFC] perf: need to expose sched_clock to correlate user samples
 with kernel samples
References: <CABPqkBQALeD=iO9x-N0nw+shhqa1kmUaj=sCvx+MvoAPGQ-y9A@mail.gmail.com> <1350408232.2336.42.camel@laptop> <1359728280.8360.15.camel@hornet> <CABPqkBSVeU_JP2KpVZLepKDJX=-g6A45Y5MoNphd6+DaU2PQzQ@mail.gmail.com> <51118797.9080800@linaro.org> <alpine.LFD.2.02.1302182132230.22263@ionos> <5123C3AF.8060100@linaro.org> <1361356160.10155.22.camel@laptop> <51285BF1.2090208@linaro.org> <1361801441.4007.40.camel@laptop> <CABPqkBS4TELhoUGrO+moca2fPUoqGjiYCdHJc=H8CjLomPWWDQ@mail.gmail.com> <1363291021.3100.144.camel@hornet> <51586315.7080006@gmail.com> <5159D221.70304@linaro.org> <515A0A3A.2040105@gmail.com> <CABPqkBStMd-VT8aoPhFV-rxiLOrH7h2HtS9O9FBkd+ggd5X+xQ@mail.gmail.com> <515C34BF.6060508@gmail.com> <CABPqkBS_z8zzSn=N_Q+AGbo1kV2EMOoF4dz2Aze=rPNB2n_n2g@mail.gmail.com>
In-Reply-To: <CABPqkBS_z8zzSn=N_Q+AGbo1kV2EMOoF4dz2Aze=rPNB2n_n2g@mail.gmail.com>
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On 4/3/13 8:00 AM, Stephane Eranian wrote:
>> What's the advantage of changing apps -- like the JIT compiler -- to emit
>> perf based timestamps versus having perf emit existing timestamps? ie.,
>> monotonic and realtime clocks already have vdso mappings for userspace with
>> well known performance characteristics. Why not have perf convert its
>> perf_clock timestamps into monotonic or realtime when dumping events?
>>
> Can monotonic timestamps be obtained from NMI context in the kernel?

I don't understand the context of the question.

I am not suggesting perf_clock be changed. I am working on correlating 
existing perf_clock timestamps to clocks typically used by apps 
(REALTIME and time-of-day but also applies to MONOTONIC).

You are wanting the reverse -- have apps emit perf_clock timestamps. I 
was just wondering what is the advantage of this approach?

David

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