* John Stultz <[email protected]> wrote:
> From: Catalin Marinas <[email protected]>
>
> 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 <[email protected]>
> Acked-by: Arnd Bergmann <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Richard Cochran <[email protected]>
> Cc: Prarit Bhargava <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> [jstultz: commit log tweaks]
> Signed-off-by: John Stultz <[email protected]>
> ---
> include/linux/jiffies.h | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
> index 265e2c3..a2134be 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))
> +#else
> +#define ACTHZ (HZ << 8)
> +#endif
The ACTHZ naming ugliness slipped past me. 'ACT' can mean so
many things - please improve it to something more obvious, like
'REAL_HZ' or 'KERNEL_HZ'.
Also, we tend to write such #if/#else/#endif patterns as:
#if FOO
# define BAR
#else
# define BAZ
#endif
Thanks,
Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
