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

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Message-ID: <20090414212236.GC5968@nowhere>
Date:	Tue, 14 Apr 2009 23:22:37 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	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>
Subject: Re: [PATCH] tracing/lockdep: turn lock->name into an array

On Tue, Apr 14, 2009 at 12:27:54PM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Tue, 2009-04-14 at 00:42 +0200, Frederic Weisbecker wrote:
> > > > +#define LOCK_NAME_SIZE       25
> > > 
> > > 
> > > 
> > > This constant may look a bit weird.
> > > I just started with the assumption that a full lock name
> > > will rarely exceed this length.
> > > 
> > > If you agree with it, I will expand the conversion of lockdep
> > > TRACE_FORMAT to TRACE_EVENTS with the same assumption.
> > > So that we will be able to use filters with locks events.
> > 
> > I really really hate this.
> > 
> > if you pick a size on the top end so that all lock->name's fit in, 
> > you're wasting heaps of space, if you pick a median length, 
> > everything will get truncated.
> > 
> > If you're going to do a copy, just do the print into the buffer by 
> > using _FORMAT and be done with it.
> 
> what i suggested was a variable length field. That solves the size 
> issue. The ring-buffer supports variable size records anyway.
> 
> 	Ingo



Indeed. That's how I plan to change it.
It can become the main new __string() field concept
that we talked about.

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