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: 32+ 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
2014-11-27 15:05 ` Pawel Moll
2014-12-11 13:39 ` Pawel Moll
2015-01-05 13:01 ` Peter Zijlstra
2015-01-21 15:47 ` Pawel Moll
2015-01-05 13:00 ` Peter Zijlstra
2015-01-21 15:52 ` Pawel Moll
2015-01-21 19:48 ` Pawel Moll
2015-01-21 20:07 ` Pawel Moll
2015-01-16 12:41 ` Adrian Hunter
2015-01-21 20:27 ` [PATCH v5] " Pawel Moll
2015-02-02 16:52 ` Pawel Moll
[not found] ` <CAN+dfcT_6zZZ4oeyngUE5N0Wtx2B9CvXsfU71m+cuyXpq2KBdw@mail.gmail.com>
2015-02-03 9:20 ` Pawel Moll
2015-02-11 16:12 ` Peter Zijlstra
2015-02-12 10:04 ` Adrian Hunter
2015-02-12 10:28 ` Peter Zijlstra [this message]
2015-02-12 15:38 ` Peter Zijlstra
2015-02-13 0:25 ` John Stultz
2015-02-13 7:07 ` Adrian Hunter
2014-11-06 16:51 ` [PATCH v4 2/3] perf: Userspace event Pawel Moll
2015-01-05 13:12 ` Peter Zijlstra
2015-01-21 16:01 ` Pawel Moll
2014-11-06 16:51 ` [PATCH v4 3/3] perf: Sample additional clock value Pawel Moll
2015-01-05 13:45 ` Peter Zijlstra
2015-01-05 19:17 ` John Stultz
2015-01-21 17:12 ` Pawel Moll
2015-01-21 17:44 ` John Stultz
2015-01-21 17:54 ` Pawel Moll
2015-01-21 18:05 ` John Stultz
2015-01-23 17:06 ` Pawel Moll
2015-01-23 18:05 ` David Ahern
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