linux-kernel - Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108

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Message-ID: <450ADC65.5020802@am.sony.com>
Date:	Fri, 15 Sep 2006 10:01:25 -0700
From:	Tim Bird <tim.bird@...sony.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	karim@...rsys.com, Roman Zippel <zippel@...ux-m68k.org>,
	Ingo Molnar <mingo@...e.hu>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tom Zanussi <zanussi@...ibm.com>, ltt-dev@...fik.org,
	Michel Dagenais <michel.dagenais@...ymtl.ca>
Subject: Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108

Alan Cox wrote:
> Ar Gwe, 2006-09-15 am 10:35 -0400, ysgrifennodd Karim Yaghmour:
>> @@ -1709,6 +1712,7 @@ switch_tasks:
>>    		++*switch_count;
>>
>>    		prepare_arch_switch(rq, next);
>> +		TRACE_SCHEDCHANGE(prev, next);
>>    		prev = context_switch(rq, prev, next);
>>    		barrier();
>
> All we appear to lack is systemtap ability to parse debug data so it can
> be told "trace on line 9 of sched.c and record rq and next"

If the latter is a suggestion for how an out-of-tree rule for a
tracepoint definition should look, it's a terrible one.
Alan's example is much more fragile, from a maintenance perspective,
than Karim's.  Plus, it's much more difficult to implement, whether
you plan to inject no-ops at compile time, just record locations and
stack offsets, or actually place some tracing code (heaven forbid)
that the compiler could optimize for that context.

I still think that this is off-topic for the patch posted.  I think we
should debate the implementation of tracepoints/markers when someone posts a
patch for some.  I think it's rather scurrilous to complain about
code NOT submitted.  Ingo has even mis-characterized the not-submitted
instrumentation patch, by saying it has 350 tracepoints when it has no
such thing.  I counted 58 for one architecture (with only 8 being
arch-specific).
 -- Tim

=============================
Tim Bird
Architecture Group Chair, CE Linux Forum
Senior Staff Engineer, Sony Electronics
=============================

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