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

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Message-ID: <4A03181D.50900@am.sony.com>
Date:	Thu, 7 May 2009 10:19:25 -0700
From:	Tim Bird <tim.bird@...sony.com>
To:	Kevin Hilman <khilman@...prootsystems.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: How to use a different sched_clock() for ftrace on omap?

Kevin Hilman wrote:
> Tim Bird <tim.bird@...sony.com> writes:
> 
>> 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.
>>
>> Unfortunately, I'm not sure the best way to use my special one, in place
>> of a common one in arch/arm/plat-omap/common.c
> 
> Hi Tim,
> 
> If you're comiling mach-omap1/time.c than you've enabled the
> higher-resolution MPU timer with CONFIG_OMAP_MPU_TIMER, right?

Yes.

> In that case, you could make the one in plat-omap/common.c inside and
> #ifndef CONFIG_OMAP_MPU_TIMER and put the new one in the MPU_TIMER
> code.
> 
> To be complete, you should add the same to the mach-omap2/timer-gp.c
> as well.

I was trying to avoid using #ifdefs, but maybe in this case it
makes sense.  There are tradeoffs in using the different timers
(nicely described in plat-omap/Kconfig help entries), so IMHO it
would be good to make this a config preference.

I'll work up a patch in this style and send it along.
 -- Tim


=============================
Tim Bird
Architecture Group Chair, CE Linux Forum
Senior Staff Engineer, Sony Corporation of America
=============================

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