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

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Date:	Thu, 18 Sep 2014 11:48:52 -0400
From:	Christopher Covington <cov@...eaurora.org>
To:	Pawel Moll <pawel.moll@....com>
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>,
	Vince Weaver <vincent.weaver@...ne.edu>
Subject: Re: [PATCH 0/2] perf: User/kernel time correlation and event generation

On 09/18/2014 11:07 AM, Pawel Moll wrote:
> 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?

Nope--reading that page and trying out examples is pretty much how I learned
to use perf events. Another great Vince Weaver perf events contribution is the
test suite, if you're not already using it.

https://github.com/deater/perf_event_tests

Christopher

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