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authorJohn Stultz <john.stultz@linaro.org>2015-04-01 20:34:39 -0700
committerIngo Molnar <mingo@kernel.org>2015-04-03 08:18:35 +0200
commit8e56f33f8439b2f8e7f4ae7f3d0bfe683ecc3b09 (patch)
tree34bfce3a900d5b38f8c3af685bc1841356c9bb19 /kernel/time
parent0fa88cb4b82b5cf7429bc1cef9db006ca035754e (diff)
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.c7
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)
{