From: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
To: Adrian Hunter <adrian.hunter-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Cc: Pawel Moll <pawel.moll-5wv7dgnIgG8@public.gmane.org>,
ajh mls <ajhmls-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
Richard Cochran
<richardcochran-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
Steven Rostedt <rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org>,
Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
Paul Mackerras <paulus-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org>,
Arnaldo Carvalho de Melo
<acme-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
John Stultz <john.stultz-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>,
Masami Hiramatsu
<masami.hiramatsu.pt-FCd8Q96Dh0JBDgjK7y7TUQ@public.gmane.org>,
Christopher Covington
<cov-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>,
Namhyung Kim <namhyung-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
David Ahern <dsahern-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
Tomeu Vizoso <tomeu-XCtybt49RKsYaV1qd6yewg@public.gmane.org>,
"linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: Re: [PATCH v5] perf: Use monotonic clock as a source for timestamps
Date: Thu, 12 Feb 2015 11:28:14 +0100 [thread overview]
Message-ID: <20150212102814.GK2896@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <54DC7AC6.5010605-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
On Thu, Feb 12, 2015 at 12:04:54PM +0200, Adrian Hunter wrote:
> On 11/02/15 18:12, Peter Zijlstra wrote:
> >
> > How about something like the below? I _think_ it should mostly work for
> > x86, where the tsc is a 64bit wide cycle counter.
>
> It would have to be based on CLOCK_MONOTONIC_RAW not CLOCK_MONOTONIC
Why?
> and you would have to check the clocksource is TSC.
It implicitly does that; it has that sched_clock_stable() thing, but
yeah I suppose someone could change the clocksource even though the tsc
is stable.
Not using TSC when its available is quite crazy though.. but sure.
> Why is CLOCK_MONOTONIC preferred anyway - I would have thought any
> adjustment would skew performance timings?
Because you can do inter-machine stuff with MONOTONIC and that's
entirely impossible with MONO_RAW.
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Pawel Moll <pawel.moll@arm.com>, ajh mls <ajhmls@gmail.com>,
Richard Cochran <richardcochran@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>, Paul Mackerras <paulus@samba.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
John Stultz <john.stultz@linaro.org>,
Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
Christopher Covington <cov@codeaurora.org>,
Namhyung Kim <namhyung@kernel.org>,
David Ahern <dsahern@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Tomeu Vizoso <tomeu@tomeuvizoso.net>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>
Subject: Re: [PATCH v5] perf: Use monotonic clock as a source for timestamps
Date: Thu, 12 Feb 2015 11:28:14 +0100 [thread overview]
Message-ID: <20150212102814.GK2896@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <54DC7AC6.5010605@intel.com>
On Thu, Feb 12, 2015 at 12:04:54PM +0200, Adrian Hunter wrote:
> On 11/02/15 18:12, Peter Zijlstra wrote:
> >
> > How about something like the below? I _think_ it should mostly work for
> > x86, where the tsc is a 64bit wide cycle counter.
>
> It would have to be based on CLOCK_MONOTONIC_RAW not CLOCK_MONOTONIC
Why?
> and you would have to check the clocksource is TSC.
It implicitly does that; it has that sched_clock_stable() thing, but
yeah I suppose someone could change the clocksource even though the tsc
is stable.
Not using TSC when its available is quite crazy though.. but sure.
> Why is CLOCK_MONOTONIC preferred anyway - I would have thought any
> adjustment would skew performance timings?
Because you can do inter-machine stuff with MONOTONIC and that's
entirely impossible with MONO_RAW.
next prev parent reply other threads:[~2015-02-12 10:28 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-06 16:51 [PATCH v4 0/3] perf: User/kernel time correlation and event generation Pawel Moll
2014-11-06 16:51 ` [PATCH v4 1/3] perf: Use monotonic clock as a source for timestamps Pawel Moll
[not found] ` <1415292718-19785-2-git-send-email-pawel.moll-5wv7dgnIgG8@public.gmane.org>
2014-11-27 15:05 ` Pawel Moll
2014-11-27 15:05 ` Pawel Moll
[not found] ` <1417100750.4371.1.camel-5wv7dgnIgG8@public.gmane.org>
2014-12-11 13:39 ` Pawel Moll
2014-12-11 13:39 ` Pawel Moll
[not found] ` <1418305153.4037.1.camel-5wv7dgnIgG8@public.gmane.org>
2015-01-05 13:01 ` Peter Zijlstra
2015-01-05 13:01 ` Peter Zijlstra
2015-01-21 15:47 ` Pawel Moll
2015-01-16 12:41 ` Adrian Hunter
2015-01-16 12:41 ` Adrian Hunter
2015-01-21 20:27 ` [PATCH v5] " Pawel Moll
2015-01-21 20:27 ` Pawel Moll
[not found] ` <1421872037-12559-1-git-send-email-pawel.moll-5wv7dgnIgG8@public.gmane.org>
2015-02-02 16:52 ` Pawel Moll
2015-02-02 16:52 ` Pawel Moll
[not found] ` <CAN+dfcT_6zZZ4oeyngUE5N0Wtx2B9CvXsfU71m+cuyXpq2KBdw@mail.gmail.com>
[not found] ` <CAN+dfcT_6zZZ4oeyngUE5N0Wtx2B9CvXsfU71m+cuyXpq2KBdw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-02-03 9:20 ` Pawel Moll
2015-02-03 9:20 ` Pawel Moll
[not found] ` <1422955245.4944.26.camel-5wv7dgnIgG8@public.gmane.org>
2015-02-11 16:12 ` Peter Zijlstra
2015-02-11 16:12 ` Peter Zijlstra
[not found] ` <20150211161256.GH2896-IIpfhp3q70z/8w/KjCw3T+5/BudmfyzbbVWyRVo5IupeoWH0uzbU5w@public.gmane.org>
2015-02-12 10:04 ` Adrian Hunter
2015-02-12 10:04 ` Adrian Hunter
[not found] ` <54DC7AC6.5010605-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2015-02-12 10:28 ` Peter Zijlstra [this message]
2015-02-12 10:28 ` Peter Zijlstra
[not found] ` <20150212102814.GK2896-IIpfhp3q70z/8w/KjCw3T+5/BudmfyzbbVWyRVo5IupeoWH0uzbU5w@public.gmane.org>
2015-02-12 15:38 ` Peter Zijlstra
2015-02-12 15:38 ` Peter Zijlstra
[not found] ` <20150212153808.GR24151-ndre7Fmf5hadTX5a5knrm8zTDFooKrT+cvkQGrU6aU0@public.gmane.org>
2015-02-13 0:25 ` John Stultz
2015-02-13 0:25 ` John Stultz
2015-02-13 7:07 ` Adrian Hunter
2015-02-13 7:07 ` Adrian Hunter
2015-01-05 13:00 ` [PATCH v4 1/3] " Peter Zijlstra
[not found] ` <20150105130035.GP30905-ndre7Fmf5hadTX5a5knrm8zTDFooKrT+cvkQGrU6aU0@public.gmane.org>
2015-01-21 15:52 ` Pawel Moll
2015-01-21 15:52 ` Pawel Moll
[not found] ` <1421855543.14076.68.camel-5wv7dgnIgG8@public.gmane.org>
2015-01-21 19:48 ` Pawel Moll
2015-01-21 19:48 ` Pawel Moll
[not found] ` <1421869684.14076.105.camel-5wv7dgnIgG8@public.gmane.org>
2015-01-21 20:07 ` Pawel Moll
2015-01-21 20:07 ` Pawel Moll
[not found] ` <1415292718-19785-1-git-send-email-pawel.moll-5wv7dgnIgG8@public.gmane.org>
2014-11-06 16:51 ` [PATCH v4 2/3] perf: Userspace event Pawel Moll
2014-11-06 16:51 ` Pawel Moll
[not found] ` <1415292718-19785-3-git-send-email-pawel.moll-5wv7dgnIgG8@public.gmane.org>
2015-01-05 13:12 ` Peter Zijlstra
2015-01-05 13:12 ` Peter Zijlstra
[not found] ` <20150105131237.GR30905-ndre7Fmf5hadTX5a5knrm8zTDFooKrT+cvkQGrU6aU0@public.gmane.org>
2015-01-21 16:01 ` Pawel Moll
2015-01-21 16:01 ` Pawel Moll
2014-11-06 16:51 ` [PATCH v4 3/3] perf: Sample additional clock value Pawel Moll
[not found] ` <1415292718-19785-4-git-send-email-pawel.moll-5wv7dgnIgG8@public.gmane.org>
2015-01-05 13:45 ` Peter Zijlstra
2015-01-05 13:45 ` Peter Zijlstra
2015-01-05 19:17 ` John Stultz
[not found] ` <20150105134514.GS30905-ndre7Fmf5hadTX5a5knrm8zTDFooKrT+cvkQGrU6aU0@public.gmane.org>
2015-01-21 17:12 ` Pawel Moll
2015-01-21 17:12 ` Pawel Moll
[not found] ` <1421860365.14076.91.camel-5wv7dgnIgG8@public.gmane.org>
2015-01-21 17:44 ` John Stultz
2015-01-21 17:44 ` John Stultz
[not found] ` <CALAqxLV6ggCO81ntWuYuDjrqNeMePkZBpq92G9-iwMHm7ONuFg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-01-21 17:54 ` Pawel Moll
2015-01-21 17:54 ` Pawel Moll
[not found] ` <1421862883.14076.99.camel-5wv7dgnIgG8@public.gmane.org>
2015-01-21 18:05 ` John Stultz
2015-01-21 18:05 ` John Stultz
2015-01-23 17:06 ` Pawel Moll
2015-01-23 17:06 ` Pawel Moll
[not found] ` <1422032767.14076.151.camel-5wv7dgnIgG8@public.gmane.org>
2015-01-23 18:05 ` David Ahern
2015-01-23 18:05 ` David Ahern
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