linux-kernel - Re: [PATCH] omap: add sched_clock for omap1 based on MPU timer

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Message-ID: <87eiug50q1.fsf@deeprootsystems.com>
Date:	Fri, 22 May 2009 13:41:58 -0700
From:	Kevin Hilman <khilman@...prootsystems.com>
To:	Tim Bird <tim.bird@...sony.com>
Cc:	linux kernel <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.arm.linux.org.uk>,
	linux-omap-open-source@...ux.omap.com
Subject: Re: [PATCH] omap: add sched_clock for omap1 based on MPU timer

Tim Bird <tim.bird@...sony.com> writes:

> Define a higher-resolution sched_clock for OMAP
> using the MPU timer, when it is configured on.
>
> This produces better results from ftrace.
>
> Signed-off-by: Tim Bird <tim.bird@...sony.com>
> ---
>  arch/arm/mach-omap1/time.c  |    9 +++++++++
>  arch/arm/plat-omap/common.c |    2 ++
>  2 files changed, 11 insertions(+)
>
> --- 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;
> +}
> +

Minor nit: I think this should rather look something like:

     cycle_t c;

     c = clocksource_read(&clocksource_mpu);
     return cyc2ns(&clocksource_mpu, c);

This way, if the clocksource implementation is changed (to use a
different timer for example) this doesn't have to be changed as well.

Kevin

>  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
> @@ -199,6 +199,7 @@ static struct clocksource clocksource_32
>  	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
>  };
>
> +#ifndef CONFIG_OMAP_MPU_TIMER
>  /*
>   * 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.
> @@ -211,6 +212,7 @@ unsigned long long notrace sched_clock(v
>  	ret = (ret * clocksource_32k.mult_orig) >> clocksource_32k.shift;
>  	return ret;
>  }
> +#endif
>
>  static int __init omap_init_clocksource_32k(void)
>  {

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