linux-kernel - Re: [PATCH] tracing/lockdep: turn lock->name into an array

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Message-ID: <20090414002403.GM5977@nowhere>
Date:	Tue, 14 Apr 2009 02:24:04 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Zhaolei <zhaolei@...fujitsu.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Li Zefan <lizf@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] tracing/lockdep: turn lock->name into an array

On Tue, Apr 14, 2009 at 01:01:10AM +0200, Ingo Molnar wrote:
> 
> * Frederic Weisbecker <fweisbec@...il.com> wrote:
> 
> >  	TP_STRUCT__entry(
> > -		__field(const char *, name)
> > +		__array(char, name, LOCK_NAME_SIZE)
> >  		__field(unsigned long, wait_usec)
> >  		__field(unsigned long, wait_nsec_rem)
> >  	),
> 
> Hm. These constants tend to grow - 25 will certainly be too narrow. 
> But increasing it increases the record size as well.


Yeah, that's why I'm not sure about the right size.

 
> I think we'll need an embedded __string() type, with a length field 
> (but still also zero-delimited, for convenience), hm?


Indeed. It tends to be a repetitive pattern.
Also, may be we can use an undefined array size on the structure
for the __string field.
We already do so with the old style trace_printk entry and may be
some others. Extending TRACE_EVENT to support it shouldn't be a big deal.

I'll just wait for Steven changes and try to do that.


> 	Ingo

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