linux-kernel - Re: [PATCH 0/2] perf: User/kernel time correlation and event generation

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Date:	Thu, 18 Sep 2014 16:07:17 +0100
From:	Pawel Moll <pawel.moll@....com>
To:	Christopher Covington <cov@...eaurora.org>
Cc:	Richard Cochran <richardcochran@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	John Stultz <john.stultz@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH 0/2] perf: User/kernel time correlation and event
 generation

On Thu, 2014-09-18 at 16:02 +0100, Christopher Covington wrote:
> Hi Pawel,
> 
> On 09/18/2014 10:34 AM, Pawel Moll wrote:
> > Greetings,
> > 
> > This is a second spin of the short series posted last week:
> > 
> > http://www.spinics.net/lists/kernel/msg1824419.html
> > 
> > The first patch adds an additional timestamp field in the perf
> > sample data, which can be requested for any perf event along
> > with normal PERF_SAMPLE_TIME. Events with both values appearing
> > periodically in the perf data allow user code to translate
> > raw monotonic time (obtained via POSIX clock API) to sched_clock
> > domain. Although any perf event can be used, the natural choice
> > would be a sched_switch trace event (for processes with root
> > permissions) or a hrtimer-based PERF_COUNT_SW_CPU_CLOCK.
> > 
> > It didn't attract any comments previously, so is just re-posted
> > without any changes.
> > 
> > The second patch, functionally orthogonal but complementing
> > the first one, builds on the ftrace "trace_maker" idea. It adds
> > a ioctl that can be used to inject a userspace-generated data
> > into the perf buffer. It provides base for printf-like
> > functionality in perf world. If used with the previous patch,
> > it can be also used to provide synchronisation points for sched
> > vs. raw monotonic time stamps correlation.
> > 
> > First version of the patch was taking a zero-terminated string
> > as an argument. Now it is taking a custom structure with "type"
> > and "size" integer fields followed by data. Type value "0"
> > is defined as a zero-terminated string (although size, including
> > the NULL character, must still be provided), but meaning of data
> > for other types is of no interest for the kernel. The intention
> > is to host a list of "well known" types (with reference parsers
> > for them) in the user perf tool code.
> 
> Would it be possible for you to also update the corresponding man pages?
> 
> https://www.kernel.org/doc/man-pages/

I must admit I haven't thought of that, but of course - if the changes
are accepted I'll send patches to the perf_event_open(2) man page. Any
others you had in mind?

Pawel

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