linux-kernel - Re: [PATCH 2/8] tracing: create automated trace defines

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Date:	Thu, 16 Apr 2009 19:44:11 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Theodore Tso <tytso@....edu>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@....de>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Zhaolei <zhaolei@...fujitsu.com>, Li Zefan <lizf@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	"Frank Ch. Eigler" <fche@...stic.org>,
	Tom Zanussi <tzanussi@...il.com>,
	Jiaying Zhang <jiayingz@...gle.com>,
	Michael Rubin <mrubin@...gle.com>,
	Martin Bligh <mbligh@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Neil Horman <nhorman@...driver.com>,
	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 2/8] tracing: create automated trace defines

* Jeremy Fitzhardinge (jeremy@...p.org) wrote:
> Mathieu Desnoyers wrote:
>> Is your only problem the fact that tracepoints include rcupdate.h ?
>
> No.  That was the first roadblock, which caused massive cyclic  
> dependencies between includes and consequent failure to define  
> everything required.  I solved that by pushing __DO_TRACE out of line.   
> Everything since then is a separate issue.
>
>>  This
>> can easily be solved by moving rcu_read_(un)lock_sched_notrace to a
>> rcu-update-<insert meaningful name here> and include this header in
>> rcupdate.h and tracepoint.h.
>>   
> I suppose, but I think pushing __do_trace_##name out of line is cleaner  
> anyway.  And I think it's very important that tracepoint.h have a  
> *absolutely minimal* #include set, so that it can be safely included in  
> as many contexts as possible.  asm/paravirt.h is complex enough as it  
> is, and I really don't want tracepoint bringing in any extra headers at  
> all.  linux/types.h is about the only acceptable one.
>
>> If by doing these modifications we succeed in keeping the "void"
>> parameters working _and_ make your stuff to compile, I think we would
>> have done something great. :-)
>>   
>
> The void issue is irritating, but relatively minor compared to the rest.  
> If everything else gets solved except for the need to pass a dummy param 
> to no-arg tracepoints, then I think it'll be a generally useful facility.
>

The other point I dislike about the out-of-line approach is that the
tracer will suffer from a pointless supplementary function call at each
event. Given how slow function calls are, at least on x86, I'd prefer
leaving the handler call chain inline, unless there is a very strong
reason not to do so.

I'll come up with a patch that leaves the tracepoint inline, but fixes
the header dependency.

Mathieu

>    J
>

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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