linux-kernel - Re: [RFC PATCH 16/22 -v2] add get_monotonic

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Date:	Wed, 16 Jan 2008 12:45:14 -0800
From:	Tim Bird <tim.bird@...sony.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sam Ravnborg <sam@...nborg.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Daniel Walker <dwalker@...sta.com>
Subject: Re: [RFC PATCH 16/22 -v2] add get_monotonic_cycles

Mathieu Desnoyers wrote:
> If LTTng is already ported to your specific kernel, the learning-curve
> is not big at all. Here is what the latency_tracer over LTTng guide
> could look like :
> 
> Well, once you have LTTng in your kernel and have compiled and installed
> the ltt-control and lttv packages (configure, make, make install), all
> that would be needed is :
> 
> (there may be some bits in the QUICKSTART GUIDE on
> http://ltt.polymtl.ca, like adding the debugfs mount to fstab and make sure
> the LTTng modules are loaded)
> 
> #arm all the markers
> ltt-armall
> #start lttng tracing
> lttctl -n test -t /tmp/trace1 -d -l /mnt/debugfs/ltt
> 
> -> start latency tracer
> -> stop latency tracer
> -> trigger latency tracer dump
> 
> While the tracing is active, trigger the condition...
> 
> (rince, repeat, can handle multiple latency tracer dumps)
> 
> #stop lttng tracing
> lttctl -n test -R
> #disarm all markers
> ltt-disarmall
> 
> You can easily test the trace with :
> lttv -m textDump -t /tmp/trace1
> 
> Your users would issue something like :
> 
> lttv -m latencytracerDump -t /tmp/trace1

No offense, but this is still quite a bit harder than:

echo 1 >/proc/something
... wait a bit ...
cat /proc/something

(substitute /sys or /debugfs where appropriate)

Having to compile something (besides the kernel) for the target
is sometimes a major hassle.  I avoided it completely with KFT.
 -- Tim

=============================
Tim Bird
Architecture Group Chair, CE Linux Forum
Senior Staff Engineer, Sony Corporation of America
=============================

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