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clocksource: Improve comment explaining clocks_calc_max_nsecs()'s 50% safety margin

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Ingo noted that the description of clocks_calc_max_nsecs()'s
50% safety margin was somewhat circular. So this patch tries
to improve the comment to better explain what we mean by the
50% safety margin and why we need it.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1427945681-29972-20-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
John Stultz 2015-04-01 20:34:39 -07:00 committed by Ingo Molnar
parent 0fa88cb4b8
commit 8e56f33f84
1 changed files with 5 additions and 2 deletions
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7
kernel/time/clocksource.c
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@ -472,8 +472,11 @@ static u32 clocksource_max_adjustment(struct clocksource *cs)
* @max_cyc: maximum cycle value before potential overflow (does not include
* any safety margin)
*
* NOTE: This function includes a safety margin of 50%, so that bad clock values
* can be detected.
* NOTE: This function includes a safety margin of 50%, in other words, we
* return half the number of nanoseconds the hardware counter can technically
* cover. This is done so that we can potentially detect problems caused by
* delayed timers or bad hardware, which might result in time intervals that
* are larger then what the math used can handle without overflows.
*/
u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
{