From 7d2f944a2b836c69a9d260a0a5f0d1720d57fdff Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 11 Nov 2009 14:05:29 +0000 Subject: clocksource: Provide a generic mult/shift factor calculation MIPS has two functions to calculcate the mult/shift factors for clock sources and clock events at run time. ARM needs such functions as well. Implement a function which calculates the mult/shift factors based on the frequencies to which and from which is converted. The function also has a parameter to specify the minimum conversion range in seconds. This range is guaranteed not to produce a 64bit overflow when a value is multiplied with the calculated mult factor. The larger the conversion range the less becomes the conversion accuracy. Provide two inline wrappers which handle clock events and clock sources. For clock events the "from" frequency is nano seconds per second which corresponds to 1GHz and "to" is the device frequency. For clock sources "from" is the device frequency and "to" is nano seconds per second. Signed-off-by: Thomas Gleixner Tested-by: Mikael Pettersson Acked-by: Ralf Baechle Acked-by: Linus Walleij Cc: John Stultz LKML-Reference: <20091111134229.766673305@linutronix.de> --- include/linux/clocksource.h | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'include/linux/clocksource.h') diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h index 83d2fbd81b93..f57f88250526 100644 --- a/include/linux/clocksource.h +++ b/include/linux/clocksource.h @@ -279,6 +279,16 @@ extern void clocksource_resume(void); extern struct clocksource * __init __weak clocksource_default_clock(void); extern void clocksource_mark_unstable(struct clocksource *cs); +extern void +clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 minsec); + +static inline void +clocksource_calc_mult_shift(struct clocksource *cs, u32 freq, u32 minsec) +{ + return clocks_calc_mult_shift(&cs->mult, &cs->shift, freq, + NSEC_PER_SEC, minsec); +} + #ifdef CONFIG_GENERIC_TIME_VSYSCALL extern void update_vsyscall(struct timespec *ts, struct clocksource *c); extern void update_vsyscall_tz(void); -- cgit v1.2.3 From 98962465ed9e6ea99c38e0af63fe1dcb5a79dc25 Mon Sep 17 00:00:00 2001 From: Jon Hunter Date: Tue, 18 Aug 2009 12:45:10 -0500 Subject: nohz: Prevent clocksource wrapping during idle The dynamic tick allows the kernel to sleep for periods longer than a single tick, but it does not limit the sleep time currently. In the worst case the kernel could sleep longer than the wrap around time of the time keeping clock source which would result in losing track of time. Prevent this by limiting it to the safe maximum sleep time of the current time keeping clock source. The value is calculated when the clock source is registered. [ tglx: simplified the code a bit and massaged the commit msg ] Signed-off-by: Jon Hunter Cc: John Stultz LKML-Reference: <1250617512-23567-2-git-send-email-jon-hunter@ti.com> Signed-off-by: Thomas Gleixner --- include/linux/clocksource.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/linux/clocksource.h') diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h index f57f88250526..279c5478e8a6 100644 --- a/include/linux/clocksource.h +++ b/include/linux/clocksource.h @@ -151,6 +151,7 @@ extern u64 timecounter_cyc2time(struct timecounter *tc, * subtraction of non 64 bit counters * @mult: cycle to nanosecond multiplier * @shift: cycle to nanosecond divisor (power of two) + * @max_idle_ns: max idle time permitted by the clocksource (nsecs) * @flags: flags describing special properties * @vread: vsyscall based read * @resume: resume function for the clocksource, if necessary @@ -168,6 +169,7 @@ struct clocksource { cycle_t mask; u32 mult; u32 shift; + u64 max_idle_ns; unsigned long flags; cycle_t (*vread)(void); void (*resume)(void); -- cgit v1.2.3