linux-kernel - Re: [PATCH] Remove obsolete CLOCK_TICK

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Date:	Fri, 29 Feb 2008 15:11:30 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Roman Zippel <zippel@...ux-m68k.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] Remove obsolete CLOCK_TICK_ADJUST


On Fri, 2008-02-29 at 05:49 +0100, Roman Zippel wrote:
> Hi,
> 
> Can we please clean up the current mess and get the patch below merged?

Yea. Sorry for being slow this week, had some other distractions going
on.

I'm still not happy about the granularity issue (or non-issue in your
mind), but both my version and your version of the solution are pretty
close at this point and I can rework my difference on-top of this patch
without much trouble.


> Revert bbe4d18ac2e058c56adb0cd71f49d9ed3216a405 and
> e13a2e61dd5152f5499d2003470acf9c838eab84 and remove CLOCK_TICK_ADJUST
> completely. Add a optional kernel parameter ntp_tick_adj instead to allow
> adjusting of a large base drift and thus keeping ntpd happy.
> The CLOCK_TICK_ADJUST mechanism was introduced at a time PIT was the
> primary clock, but we have a varity of clock sources now, so a global PIT
> specific adjustment makes little sense anymore.
> 
> Signed-off-by: Roman Zippel <zippel@...ux-m68k.org>

Acked-by: John Stultz <johnstul@...ibm.com>


> ---
>  include/linux/timex.h     |    9 +--------
>  kernel/time/ntp.c         |   11 ++++++++++-
>  kernel/time/timekeeping.c |    6 ++----
>  3 files changed, 13 insertions(+), 13 deletions(-)
> 
> Index: linux-2.6/include/linux/timex.h
> ===================================================================
> --- linux-2.6.orig/include/linux/timex.h
> +++ linux-2.6/include/linux/timex.h
> @@ -232,14 +232,7 @@ static inline int ntp_synced(void)
>  #else
>  #define NTP_INTERVAL_FREQ  (HZ)
>  #endif
> -
> -#define CLOCK_TICK_OVERFLOW	(LATCH * HZ - CLOCK_TICK_RATE)
> -#define CLOCK_TICK_ADJUST	(((s64)CLOCK_TICK_OVERFLOW * NSEC_PER_SEC) / \
> -					(s64)CLOCK_TICK_RATE)
> -
> -/* Because using NSEC_PER_SEC would be too easy */
> -#define NTP_INTERVAL_LENGTH ((((s64)TICK_USEC * NSEC_PER_USEC * USER_HZ) + \
> -			      CLOCK_TICK_ADJUST) / NTP_INTERVAL_FREQ)
> +#define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)
> 
>  /* Returns how long ticks are at present, in ns / 2^(SHIFT_SCALE-10). */
>  extern u64 current_tick_length(void);
> Index: linux-2.6/kernel/time/ntp.c
> ===================================================================
> --- linux-2.6.orig/kernel/time/ntp.c
> +++ linux-2.6/kernel/time/ntp.c
> @@ -42,12 +42,13 @@ long time_esterror = NTP_PHASE_LIMIT;	/*
>  long time_freq;				/* frequency offset (scaled ppm)*/
>  static long time_reftime;		/* time at last adjustment (s)	*/
>  long time_adjust;
> +long ntp_tick_adj;
> 
>  static void ntp_update_frequency(void)
>  {
>  	u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
>  				<< TICK_LENGTH_SHIFT;
> -	second_length += (s64)CLOCK_TICK_ADJUST << TICK_LENGTH_SHIFT;
> +	second_length += (s64)ntp_tick_adj << TICK_LENGTH_SHIFT;
>  	second_length += (s64)time_freq << (TICK_LENGTH_SHIFT - SHIFT_NSEC);
> 
>  	tick_length_base = second_length;
> @@ -400,3 +401,11 @@ leave:	if ((time_status & (STA_UNSYNC|ST
>  	notify_cmos_timer();
>  	return(result);
>  }
> +
> +static int __init ntp_tick_adj_setup(char *str)
> +{
> +	ntp_tick_adj = simple_strtol(str, NULL, 0);
> +	return 1;
> +}
> +
> +__setup("ntp_tick_adj=", ntp_tick_adj_setup);
> Index: linux-2.6/kernel/time/timekeeping.c
> ===================================================================
> --- linux-2.6.orig/kernel/time/timekeeping.c
> +++ linux-2.6/kernel/time/timekeeping.c
> @@ -187,8 +187,7 @@ static void change_clocksource(void)
> 
>  	clock->error = 0;
>  	clock->xtime_nsec = 0;
> -	clocksource_calculate_interval(clock,
> -		(unsigned long)(current_tick_length()>>TICK_LENGTH_SHIFT));
> +	clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
> 
>  	tick_clock_notify();
> 
> @@ -245,8 +244,7 @@ void __init timekeeping_init(void)
>  	ntp_clear();
> 
>  	clock = clocksource_get_next();
> -	clocksource_calculate_interval(clock,
> -		(unsigned long)(current_tick_length()>>TICK_LENGTH_SHIFT));
> +	clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
>  	clock->cycle_last = clocksource_read(clock);
> 
>  	xtime.tv_sec = sec;

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