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From: John Stultz <john.stultz@linaro.org>
To: Stephane Eranian <eranian@google.com>
Cc: David Ahern <dsahern@gmail.com>, 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>
Subject: Re: [RFC] perf: need to expose sched_clock to correlate user samples with kernel samples
Date: Thu, 04 Apr 2013 15:26:39 -0700	[thread overview]
Message-ID: <515DFE1F.3010106@linaro.org> (raw)
In-Reply-To: <CABPqkBRaCgb3Gp8_DT_S5rd9BcpTVeKgY2Ozk_yyAQP4W4SR1Q@mail.gmail.com>

On 04/04/2013 01:12 AM, Stephane Eranian wrote:
> On Wed, Apr 3, 2013 at 7:57 PM, John Stultz <john.stultz@linaro.org> wrote:
>> I'm not sure I follow this. If perf exported data came with CLOCK_MONOTONIC
>> timestamps, no correlation would need to be exposed.  perf would just have
>> to do the extra overhead of doing the conversion on export.
> There is no explicit export operation in perf.  You record a sample when
> the counter overflows and generates an NMI interrupt. In the NMI interrupt
> handler, the sample record is written to the sampling buffer. That is when
> the timestamp is generated. The sampling buffer is directly accessible to
> users via mmap(). The perf tool just dumps the raw sampling buffer into
> a file, no sample record is modified or even looked at. The processing
> of the samples is done offline (via perf report) and could be done on
> another machine. In other words, the perf.data file is self-contained.
Ah. Ok, I didn't realize perfs buffers were directly mmaped.  I was 
thinking perf could do the translation not at NMI time but when the 
buffer was later read by the application.  That helps explain some of 
the constraints.

thanks
-john

  reply	other threads:[~2013-04-04 22:26 UTC|newest]

Thread overview: 65+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-10-16 10:13 [RFC] perf: need to expose sched_clock to correlate user samples with kernel samples Stephane Eranian
2012-10-16 17:23 ` Peter Zijlstra
2012-10-18 19:33   ` Stephane Eranian
2012-11-10  2:04   ` John Stultz
2012-11-11 20:32     ` Stephane Eranian
2012-11-12 18:53       ` John Stultz
2012-11-12 20:54         ` Stephane Eranian
2012-11-12 22:39           ` John Stultz
2012-11-13 20:58     ` Steven Rostedt
2012-11-14 22:26       ` John Stultz
2012-11-14 23:30         ` Steven Rostedt
2013-02-01 14:18   ` Pawel Moll
2013-02-05 21:18     ` David Ahern
2013-02-05 22:13     ` Stephane Eranian
2013-02-05 22:28       ` John Stultz
2013-02-06  1:19         ` Steven Rostedt
2013-02-06 18:17           ` Pawel Moll
2013-02-13 20:00             ` Stephane Eranian
2013-02-14 10:33               ` Pawel Moll
2013-02-18 15:16                 ` Stephane Eranian
2013-02-18 18:59                   ` David Ahern
2013-02-18 20:35         ` Thomas Gleixner
2013-02-19 18:25           ` John Stultz
2013-02-19 19:55             ` Thomas Gleixner
2013-02-19 20:15               ` Thomas Gleixner
2013-02-19 20:35                 ` John Stultz
2013-02-19 21:50                   ` Thomas Gleixner
2013-02-19 22:20                     ` John Stultz
2013-02-20 10:06                       ` Thomas Gleixner
2013-02-20 10:29             ` Peter Zijlstra
2013-02-23  6:04               ` John Stultz
2013-02-25 14:10                 ` Peter Zijlstra
2013-03-14 15:34                   ` Stephane Eranian
2013-03-14 19:57                     ` Pawel Moll
2013-03-31 16:23                       ` David Ahern
2013-04-01 18:29                         ` John Stultz
2013-04-01 22:29                           ` David Ahern
2013-04-01 23:12                             ` John Stultz
2013-04-03  9:17                             ` Stephane Eranian
2013-04-03 13:55                               ` David Ahern
2013-04-03 14:00                                 ` Stephane Eranian
2013-04-03 14:14                                   ` David Ahern
2013-04-03 14:22                                     ` Stephane Eranian
2013-04-03 17:57                                       ` John Stultz
2013-04-04  8:12                                         ` Stephane Eranian
2013-04-04 22:26                                           ` John Stultz [this message]
2013-04-02  7:54                           ` Peter Zijlstra
2013-04-02 16:05                             ` Pawel Moll
2013-04-02 16:19                             ` John Stultz
2013-04-02 16:34                               ` Pawel Moll
2013-04-03 17:19                               ` Pawel Moll
2013-04-03 17:29                                 ` John Stultz
2013-04-03 17:35                                   ` Pawel Moll
2013-04-03 17:50                                     ` John Stultz
2013-04-04  7:37                                       ` Richard Cochran
2013-04-04 16:33                                         ` Pawel Moll
2013-04-04 16:29                                       ` Pawel Moll
2013-04-05 18:16                                         ` Pawel Moll
2013-04-06 11:05                                           ` Richard Cochran
2013-04-08 17:58                                             ` Pawel Moll
2013-04-08 19:05                                               ` John Stultz
2013-04-09  5:02                                                 ` Richard Cochran
2013-02-06 18:17       ` Pawel Moll
2013-06-26 16:49     ` David Ahern
2013-07-15 10:44       ` Pawel Moll

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