linux-kernel - Re: How to use a different sched

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Message-ID: <20090507135911.GD481@elte.hu>
Date:	Thu, 7 May 2009 15:59:11 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Tim Bird <tim.bird@...sony.com>,
	Ryan Mallon <ryan@...ewatersys.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	linux kernel <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.arm.linux.org.uk>
Subject: Re: How to use a different sched_clock() for ftrace on omap?


* Steven Rostedt <rostedt@...dmis.org> wrote:

> On Thu, 7 May 2009, Ingo Molnar wrote:
> 
> > 
> > * Tim Bird <tim.bird@...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
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