All of lore.kernel.org
 help / color / mirror / Atom feed
From: Ingo Molnar <mingo@kernel.org>
To: David Ahern <dsahern@gmail.com>
Cc: linux-kernel@vger.kernel.org, Pawel Moll <pawel.moll@arm.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Mike Galbraith <efault@gmx.de>, Jiri Olsa <jolsa@redhat.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Stephane Eranian <eranian@google.com>,
	John Stultz <john.stultz@linaro.org>,
	Sonny Rao <sonnyrao@chromium.org>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] perf: POSIX CLOCK_PERF to report current time value
Date: Wed, 11 Dec 2013 12:25:26 +0100	[thread overview]
Message-ID: <20131211112526.GC25541@gmail.com> (raw)
In-Reply-To: <1386707259-21725-1-git-send-email-dsahern@gmail.com>


* David Ahern <dsahern@gmail.com> wrote:

> From: Pawel Moll <pawel.moll@arm.com>
> 
> To co-relate user space events with the perf events stream
> a current (as in: "what time(stamp) is it now?") time value
> must be made available.

So I'm wondering about your earlier approach posted here:

  https://lkml.org/lkml/2011/6/7/636

I'd modify that patch the following way: instead of tracking each 
separate reason, perhaps only track timekeeping_update().

Such a tracepoint, combined with PERF_SAMPLE_TIME, would very 
accurately track external changes to GTOD (xtime).

That leaves us with tracking/correlating the regular flow of time, 
which could be achieved by another tracepoint in:

   kernel/time/timekeeping.c::do_timer()

So only two new tracepoints are needed AFAICS - and the tracepoints 
would obviously be useful for other (debugging) purposes as well. 
Would that solve the wall-clock correlation problem adequately?

Thanks,

	Ingo

  parent reply	other threads:[~2013-12-11 11:25 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-12-10 20:27 [PATCH] perf: POSIX CLOCK_PERF to report current time value David Ahern
2013-12-10 20:44 ` John Stultz
2013-12-11 12:07   ` Ingo Molnar
2013-12-11 19:37     ` John Stultz
2013-12-11 11:25 ` Ingo Molnar [this message]
2013-12-11 11:40   ` Ingo Molnar

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20131211112526.GC25541@gmail.com \
    --to=mingo@kernel.org \
    --cc=a.p.zijlstra@chello.nl \
    --cc=acme@redhat.com \
    --cc=dsahern@gmail.com \
    --cc=efault@gmx.de \
    --cc=eranian@google.com \
    --cc=fweisbec@gmail.com \
    --cc=john.stultz@linaro.org \
    --cc=jolsa@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=namhyung@kernel.org \
    --cc=pawel.moll@arm.com \
    --cc=sonnyrao@chromium.org \
    --cc=tglx@linutronix.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.