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Date: Thu, 7 May 2009 15:59:11 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Tim Bird <tim.bird@am.sony.com>, Ryan Mallon <ryan@bluewatersys.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
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Subject: Re: How to use a different sched_clock() for ftrace on omap?
Message-ID: <20090507135911.GD481@elte.hu>
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* Steven Rostedt <rostedt@goodmis.org> wrote:

> On Thu, 7 May 2009, Ingo Molnar wrote:
> 
> > 
> > * Tim Bird <tim.bird@am.sony.com> wrote:
> > 
> > > Hi all,
> > > 
> > > I've worked up a replacement sched_clock for ftrace on my omap 
> > > platform. The current sched_clock, based on the 32K timer, has low 
> > > resolution and doesn't provide very useful results.
> > 
> > hm, why dont you replace the real sched_clock() with it? High 
> > resolution sched_clock() gives (much!) better scheduling, better 
> > fairness, etc.
> 
> Probably because it is board specific, that he can not replace it. But I 
> think something like Ryan's idea would be good. Instead of aliasing, just 
> make another weak symbol.
> 
> 
> unsigned long long __attribute__((weak)) board_sched_clock(void)
> {
> 	[ original sched_clock code ]
> }
> 
> unsigned long long sched_clock(void)
> {
> 	return board_sched_clock();
> }
> 
> Then Tim could define a "board_sched_clock" that would be used 
> when that board is active.

that sounds good. Weak aliases are now generally supported in Linux, 
we excluded that one broken GCC version that messed them up.

	Ingo