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| author | John Stultz <john.stultz@linaro.org> | 2015-04-01 20:34:39 -0700 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-04-03 08:18:35 +0200 |
| commit | 8e56f33f8439b2f8e7f4ae7f3d0bfe683ecc3b09 (patch) | |
| tree | 34bfce3a900d5b38f8c3af685bc1841356c9bb19 /kernel/time | |
| parent | 0fa88cb4b82b5cf7429bc1cef9db006ca035754e (diff) | |
| download | lwn-8e56f33f8439b2f8e7f4ae7f3d0bfe683ecc3b09.tar.gz lwn-8e56f33f8439b2f8e7f4ae7f3d0bfe683ecc3b09.zip | |
clocksource: Improve comment explaining clocks_calc_max_nsecs()'s 50% safety margin
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>
Diffstat (limited to 'kernel/time')
| -rw-r--r-- | kernel/time/clocksource.c | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index c3be3c71bbad..15facb1b9c60 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -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) { |