From a7ea3bbf5d58f4df2265d312f91d5769eabc8144 Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Fri, 27 Jul 2012 14:48:09 -0400 Subject: time/jiffies: Allow CLOCK_TICK_RATE to be undefined CLOCK_TICK_RATE is a legacy constant that defines the timer device's granularity. On hardware with particularly coarse granularity, this constant is used to reduce accumulated time error when using jiffies as a clocksource, by calculating the hardware's actual tick length rather then just assuming it is 1sec/HZ. However, for the most part this is unnecessary, as most modern systems don't use jiffies for their clocksource, and their tick device is sufficiently fine grained to avoid major error. Thus, this patch allows an architecture to not define CLOCK_TICK_RATE, in which case ACTHZ defaults to (HZ << 8). Signed-off-by: Catalin Marinas Acked-by: Arnd Bergmann Cc: Richard Cochran Cc: Prarit Bhargava Cc: Andrew Morton [ Commit log & intention tweaks ] Signed-off-by: John Stultz Link: http://lkml.kernel.org/r/1343414893-45779-2-git-send-email-john.stultz@linaro.org Signed-off-by: Ingo Molnar --- include/linux/jiffies.h | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) (limited to 'include/linux/jiffies.h') diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h index 265e2c3cbd1c..7d24466fb80b 100644 --- a/include/linux/jiffies.h +++ b/include/linux/jiffies.h @@ -39,9 +39,6 @@ # error Invalid value of HZ. #endif -/* LATCH is used in the interval timer and ftape setup. */ -#define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ) /* For divider */ - /* Suppose we want to divide two numbers NOM and DEN: NOM/DEN, then we can * improve accuracy by shifting LSH bits, hence calculating: * (NOM << LSH) / DEN @@ -54,8 +51,15 @@ #define SH_DIV(NOM,DEN,LSH) ( (((NOM) / (DEN)) << (LSH)) \ + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN)) +#ifdef CLOCK_TICK_RATE +/* LATCH is used in the interval timer and ftape setup. */ +# define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ) /* For divider */ + /* HZ is the requested value. ACTHZ is actual HZ ("<< 8" is for accuracy) */ -#define ACTHZ (SH_DIV (CLOCK_TICK_RATE, LATCH, 8)) +# define ACTHZ (SH_DIV(CLOCK_TICK_RATE, LATCH, 8)) +#else +# define ACTHZ (HZ << 8) +#endif /* TICK_NSEC is the time between ticks in nsec assuming real ACTHZ */ #define TICK_NSEC (SH_DIV (1000000UL * 1000, ACTHZ, 8)) -- cgit v1.2.3 From 02ab20ae38337b99b5c29c81090f594b8fd61283 Mon Sep 17 00:00:00 2001 From: John Stultz Date: Fri, 27 Jul 2012 14:48:10 -0400 Subject: time/jiffies: Rename ACTHZ to SHIFTED_HZ Ingo noted that ACTHZ is a confusing name, and requested it be renamed, so this patch renames ACTHZ to SHIFTED_HZ to better describe it. Signed-off-by: John Stultz Cc: Prarit Bhargava Link: http://lkml.kernel.org/r/1343414893-45779-3-git-send-email-john.stultz@linaro.org Signed-off-by: Ingo Molnar --- include/linux/jiffies.h | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) (limited to 'include/linux/jiffies.h') diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h index 7d24466fb80b..82680541576d 100644 --- a/include/linux/jiffies.h +++ b/include/linux/jiffies.h @@ -55,21 +55,26 @@ /* LATCH is used in the interval timer and ftape setup. */ # define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ) /* For divider */ -/* HZ is the requested value. ACTHZ is actual HZ ("<< 8" is for accuracy) */ -# define ACTHZ (SH_DIV(CLOCK_TICK_RATE, LATCH, 8)) +/* + * HZ is the requested value. However the CLOCK_TICK_RATE may not allow + * for exactly HZ. So SHIFTED_HZ is high res HZ ("<< 8" is for accuracy) + */ +# define SHIFTED_HZ (SH_DIV(CLOCK_TICK_RATE, LATCH, 8)) #else -# define ACTHZ (HZ << 8) +# define SHIFTED_HZ (HZ << 8) #endif -/* TICK_NSEC is the time between ticks in nsec assuming real ACTHZ */ -#define TICK_NSEC (SH_DIV (1000000UL * 1000, ACTHZ, 8)) +/* TICK_NSEC is the time between ticks in nsec assuming SHIFTED_HZ */ +#define TICK_NSEC (SH_DIV(1000000UL * 1000, SHIFTED_HZ, 8)) /* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */ #define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ) -/* TICK_USEC_TO_NSEC is the time between ticks in nsec assuming real ACTHZ and */ -/* a value TUSEC for TICK_USEC (can be set bij adjtimex) */ -#define TICK_USEC_TO_NSEC(TUSEC) (SH_DIV (TUSEC * USER_HZ * 1000, ACTHZ, 8)) +/* + * TICK_USEC_TO_NSEC is the time between ticks in nsec assuming SHIFTED_HZ and + * a value TUSEC for TICK_USEC (can be set bij adjtimex) + */ +#define TICK_USEC_TO_NSEC(TUSEC) (SH_DIV(TUSEC * USER_HZ * 1000, SHIFTED_HZ, 8)) /* some arch's have a small-data section that can be accessed register-relative * but that can only take up to, say, 4-byte variables. jiffies being part of -- cgit v1.2.3