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Re: [PATCH v3] MIPS: Add a high resolution sched_clock() via cnt32_to_63

To: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Subject: Re: [PATCH v3] MIPS: Add a high resolution sched_clock() via cnt32_to_63().
From: Wu Zhangjin <wuzhangjin@gmail.com>
Date: Mon, 23 Nov 2009 09:00:35 +0800
Cc: Ralf Baechle <ralf@linux-mips.org>, Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>, linux-mips@linux-mips.org, Michal Simek <monstr@monstr.eu>
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Organization: DSLab, Lanzhou University, China
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <b08d39e76685878bc91d9de906d155f1daa1c985.1258894783.git.wuzhangjin@gmail.com> <4B098AE4.6090804@ru.mvista.com>
Reply-to: wuzhangjin@gmail.com
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On Sun, 2009-11-22 at 22:03 +0300, Sergei Shtylyov wrote:
> Hello.
> 
> Wu Zhangjin wrote:
> 
> > From: Wu Zhangjin <wuzhangjin@gmail.com>
> >
> > (This v3 revision incorporates with the feedbacks from Ingo, Ralf and 
> > Sergei.)
> >
> > This patch adds a cnt32_to_63() and MIPS c0 count based sched_clock(),
> > which provides high resolution. and also, one new kernel option
> > (HR_SCHED_CLOCK) is added to enable/disable this sched_clock().
> >
> > 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 v2 revision set up a
> > kernel timer to ensure the requirement of some MIPSs which have short c0
> > count period.
> >
> > Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
> > ---
> >  arch/mips/Kconfig           |   18 ++++++++++++++
> >  arch/mips/kernel/csrc-r4k.c |   55 
> > +++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 73 insertions(+), 0 deletions(-)
> >
> > diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> > index b342197..5ea55f5 100644
> > --- a/arch/mips/Kconfig
> > +++ b/arch/mips/Kconfig
> > @@ -1952,6 +1952,24 @@ config NR_CPUS
> >  source "kernel/time/Kconfig"
> >  
> >  #
> > +# High Resolution sched_clock() Configuration
> > +#
> > +
> > +config HR_SCHED_CLOCK
> > +   bool "High Resolution sched_clock()"
> > +   depends on CSRC_R4K
> > +   default n
> > +   help
> > +     This option enables the MIPS c0 count based high resolution
> > +     sched_clock().
> > +
> > +     If you need a ns precision timestamp, you are recommended to enable
> > +     this option. For example, If you are using the Ftrace subsystem to do
> > +     real time tracing, this option is needed.
> > +
> > +     If unsure, disable it.
> > +
> > +#
> >  # Timer Interrupt Frequency Configuration
> >  #
> >  
> > diff --git a/arch/mips/kernel/csrc-r4k.c b/arch/mips/kernel/csrc-r4k.c
> > index e95a3cd..e287f0d 100644
> > --- a/arch/mips/kernel/csrc-r4k.c
> > +++ b/arch/mips/kernel/csrc-r4k.c
> > @@ -10,6 +10,57 @@
> >  
> >  #include <asm/time.h>
> >  
> > +#ifdef CONFIG_HR_SCHED_CLOCK
> > +#include <linux/cnt32_to_63.h>
> > +#include <linux/timer.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 high, 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 __read_mostly tclk2ns_scale;
> > +static unsigned long __read_mostly 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 struct timer_list cnt32_to_63_keepwarm_timer;
> > +
> > +static void cnt32_to_63_keepwarm(unsigned long data)
> > +{
> > +   mod_timer(&cnt32_to_63_keepwarm_timer, round_jiffies(jiffies + data));
> > +   (void) sched_clock();
> > +}
> > +
> > +static void __init setup_sched_clock(struct clocksource *cs, unsigned long 
> > tclk)
> > +{
> > +   unsigned long long v;
> > +   unsigned long data;
> > +
> > +   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;
> > +
> > +   data = 0x80000000 / tclk * HZ;
> > +   setup_timer(&cnt32_to_63_keepwarm_timer, cnt32_to_63_keepwarm, data);
> > +   mod_timer(&cnt32_to_63_keepwarm_timer, round_jiffies(jiffies + data));
> > +}
> > +#endif     /* !CONFIG_HR_SCHED_CLOCK */
> > +
> >  static cycle_t c0_hpt_read(struct clocksource *cs)
> >  {
> >     return read_c0_count();
> > @@ -32,6 +83,10 @@ int __init init_r4k_clocksource(void)
> >  
> >     clocksource_set_clock(&clocksource_mips, mips_hpt_frequency);
> >  
> > +#ifdef CONFIG_HR_SCHED_CLOCK
> > +   setup_sched_clock(&clocksource_mips, mips_hpt_frequency);
> > +#endif
> > +
> >   
> 
>    According to CodingStyle #ifdef's in the code are frowned upon. I 
> suggest that you add an empty setup_sched_clock() definition under #else 
> above and have the call here without #ifdef. That's the preferred way of 
> doing such things...
> 

Done, thanks!

Wil resend it later.


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