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

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Message-ID: <8763gdt37p.fsf@deeprootsystems.com>
Date:	Thu, 07 May 2009 07:08:58 -0700
From:	Kevin Hilman <khilman@...prootsystems.com>
To:	Tim Bird <tim.bird@...sony.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: How to use a different sched_clock() for ftrace on omap?

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?

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.

Kevin

> Here's a patch:
>
> ---
>  arch/arm/mach-omap1/time.c  |    9 +++++++++
>  arch/arm/plat-omap/common.c |    2 +-
>  2 files changed, 10 insertions(+), 1 deletion(-)
>
> --- a/arch/arm/mach-omap1/time.c
> +++ b/arch/arm/mach-omap1/time.c
> @@ -212,6 +212,15 @@ static struct clocksource clocksource_mp
>  	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
>  };
>
> +unsigned long long notrace sched_clock(void)
> +{
> +	unsigned long long ret;
> +
> +	ret = (unsigned long long) ~omap_mpu_timer_read(1);
> +	ret = (ret * clocksource_mpu.mult_orig) >>clocksource_mpu.shift;
> +	return ret;
> +}
> +
>  static void __init omap_init_clocksource(unsigned long rate)
>  {
>  	static char err[] __initdata = KERN_ERR
> --- a/arch/arm/plat-omap/common.c
> +++ b/arch/arm/plat-omap/common.c
> @@ -203,7 +203,7 @@ static struct clocksource clocksource_32
>   * Returns current time from boot in nsecs. It's OK for this to wrap
>   * around for now, as it's just a relative time stamp.
>   */
> -unsigned long long notrace sched_clock(void)
> +__attribute__((weak)) unsigned long long notrace sched_clock_old(void)
>  {
>  	unsigned long long ret;
>
>
> Obviously, renaming the common sched_clock() to sched_clock_old() is
> a hack.
>
> I thought the __attribute__ ((weak)) would be enough to have the
> sched_clock() in common.c get out of the way, and allow my board-specific
> sched_clock() to be used.  But that didn't work.  What is the recommended
> way to specify a board-specific function at compile time?
>
> Thanks,
>  -- Tim
>
> =============================
> Tim Bird
> Architecture Group Chair, CE Linux Forum
> Senior Staff Engineer, Sony Corporation of America
> =============================
>
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