linux-kernel - Re: [PATCH] MIPS: Add a high precision sched_clock() via cnt32_to

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Date:	Fri, 20 Nov 2009 21:20:37 +0800
From:	Wu Zhangjin <wuzhangjin@...il.com>
To:	Ralf Baechle <ralf@...ux-mips.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, rostedt@...dmis.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Nicholas Mc Guire <der.herr@...r.at>,
	David Daney <ddaney@...iumnetworks.com>,
	linux-mips@...ux-mips.org, Michal Simek <monstr@...str.eu>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: Add a high precision sched_clock() via
 cnt32_to_63().

[...]
> ---
>  arch/mips/kernel/csrc-r4k.c |   37 +++++++++++++++++++++++++++++++++++++
>  1 files changed, 37 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/mips/kernel/csrc-r4k.c b/arch/mips/kernel/csrc-r4k.c
> index e95a3cd..865035d 100644
> --- a/arch/mips/kernel/csrc-r4k.c
> +++ b/arch/mips/kernel/csrc-r4k.c
> @@ -6,10 +6,45 @@
>   * Copyright (C) 2007 by Ralf Baechle
>   */
>  #include <linux/clocksource.h>
> +#include <linux/cnt32_to_63.h>
> +#include <linux/timer.h>

Sorry, <linux/timer.h> is not needed here, I have used it in the old
version with setup_timer()/mod_timer().

>  #include <linux/init.h>
>  
>  #include <asm/time.h>
>  
> +/*
> + * MIPS' sched_clock implementation.
> + *
> + * NOTE: because cnt32_to_63() needs to be called at least once per half period
> + * to work properly, and some of the MIPS' frequency is very low, perhaps a
> + * kernel timer is needed to be set up to ensure this requirement is always
> + * met. please refer to  arch/arm/plat-orion/time.c and
> + * include/linux/cnt32_to_63.h
> + */
> +static unsigned long tclk2ns_scale, tclk2ns_scale_factor;
> +
> +unsigned long long notrace sched_clock(void)
> +{
> +	unsigned long long v = cnt32_to_63(read_c0_count());
> +	return (v * tclk2ns_scale) >> tclk2ns_scale_factor;
> +}
> +
> +static void __init setup_sched_clock(struct clocksource *cs, unsigned long tclk)

the tclk is not used, I have also used it in the old version with
setup_timer()/mod_timer(). so, we can remove it for this version.

> +{
> +	unsigned long long v;
> +
> +	v = cs->mult;
> +	/*
> +	 * We want an even value to automatically clear the top bit
> +	 * returned by cnt32_to_63() without an additional run time
> +	 * instruction. So if the LSB is 1 then round it up.
> +	 */
> +	if (v & 1)
> +		v++;
> +	tclk2ns_scale = v;
> +	tclk2ns_scale_factor = cs->shift;
> +}
> +
>  static cycle_t c0_hpt_read(struct clocksource *cs)
>  {
>  	return read_c0_count();
> @@ -32,6 +67,8 @@ int __init init_r4k_clocksource(void)
>  
>  	clocksource_set_clock(&clocksource_mips, mips_hpt_frequency);
>  
> +	setup_sched_clock(&clocksource_mips, mips_hpt_frequency);
> +

And here should be setup_sched_clock(&clocksource_mips);

Regards,
	Wu Zhangjin

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