linux-kernel - Re: [PATCH 0/8] [GIT PULL] TRACE

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Message-ID: <20090415082931.GF18192@elte.hu>
Date:	Wed, 15 Apr 2009 10:29:31 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>, Theodore Tso <tytso@....edu>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@....de>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	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>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: [PATCH 0/8] [GIT PULL] TRACE_EVENT for modules


* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Steven Rostedt wrote:
>> On Tue, 14 Apr 2009, Jeremy Fitzhardinge wrote:
>>
>>   
>>> Theodore Tso wrote:
>>>     
>>>> Any chance you could support something like this?
>>>>
>>>>         
>>> I think that's already there.  I'm defining
>>> arch/x86/include/asm/paravirt-trace.h with:
>>>
>>> #ifndef _ASM_X86_PARAVIRT_TRACE_H
>>> #define _ASM_X86_PARAVIRT_TRACE_H
>>>
>>> #include <linux/tracepoint.h>
>>> #include <asm/paravirt_types.h>
>>>
>>> #undef TRACE_SYSTEM
>>> #define TRACE_SYSTEM pvops
>>>
>>> #define TRACE_INCLUDE_FILE	paravirt-trace
>>> #define TRACE_INCLUDE_PATH	asm
>>> [...]
>>>
>>>
>>> Which ends up including <asm/paravirt-trace.h>
>>>     
>>
>> Not quite. It ends up looking like
>>
>> #include "asm/paravirt-trace.h"
>>
>> As long as there is no "asm" directory in the include/trace directory, 
>> I think that is fine.
>
> OK.
>
> I'm having a bit of trouble with paravirt-trace.h when I actually 
> include it in paravirt.h.  asm/paravirt.h is itself included in 
> lots of places, and so its fairly easy to end up with cyclic 
> include dependencies which are fairly painful.  In this case I'm 
> seeing asm/paravirt.h -> linux/tracepoint.h -> linux/rcupate.h -> 
> {lots of stuff}, which gives errors like:

tracepoint.h should not include any complex headers like rcupdate.h.

> I'm wondering if there's much downside in making the code 
> __DO_TRACE() out of line so that we can make tracepoint.h have 
> absolutely minimal include dependencies?

yeah.

And besides, the rcu_read_lock_sched_notrace() there should probably 
be a preempt_disable_notrace() / preempt_enable_notrace() variant. 
(it's sligtly faster that way and we better be atomic and 
self-sufficient in tracepoints anyway)

	Ingo
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