linux-kernel - Re: [PATCH v1] MIPS: Add a high precision sched_clock() via cnt32_to

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Date:	Sun, 22 Nov 2009 13:30:26 +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 v1] MIPS: Add a high precision sched_clock() via
 cnt32_to_63().

On Sat, 2009-11-21 at 22:49 +0800, Wu Zhangjin wrote:
> From: Wu Zhangjin <wuzhangjin@...il.com>
> 
> This patch adds a cnt32_to_63() and MIPS c0 count based sched_clock(),
> which can provide high resolution. and also, two new kernel options are
> added. the HR_SCHED_CLOCK is used to enable/disable this sched_clock(),
> and the HT_SCHED_CLOCK_UPDATE is used to allow whether update the
> sched_clock() automatically or not.
> 
> Without it, the Ftrace for MIPS will give useless timestamp information.
> 
> (Because cnt32_to_63() needs to be called at least once per half period
> to work properly, Differ from the old version, this v1 revision set up a
> kernel timer to ensure the requirement of some MIPSs which have short c0
> count period.)
[...]
>  
> diff --git a/arch/mips/kernel/csrc-r4k.c b/arch/mips/kernel/csrc-r4k.c
> index e95a3cd..5048989 100644
> --- a/arch/mips/kernel/csrc-r4k.c
> +++ b/arch/mips/kernel/csrc-r4k.c
> @@ -6,10 +6,62 @@
>   * Copyright (C) 2007 by Ralf Baechle
>   */
>  #include <linux/clocksource.h>
> +#include <linux/cnt32_to_63.h>
> +#include <linux/timer.h>
>  #include <linux/init.h>
>  
>  #include <asm/time.h>
>  
> +/*
> + * MIPS' sched_clock implementation.
> + *
> + * 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 __maybe_unused tclk2ns_scale;
> +static unsigned long __maybe_unused tclk2ns_scale_factor;
> +

need to be:

#ifdef CONFIG_HR_SCHED_CLOCK
> +unsigned long long notrace sched_clock(void)
> +{
> +	unsigned long long v = cnt32_to_63(read_c0_count());
> +	return (v * tclk2ns_scale) >> tclk2ns_scale_factor;
> +}
> +
#endif

Regards,
	Wu Zhangjin

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