[PATCH] timers: Clarify usleep_range() function comment

From: Bjorn Helgaas
Date: Tue May 31 2016 - 17:23:19 EST

Update the usleep_range() function comment to make it clear that it can
only be used in non-atomic context.

Previously we claimed usleep_range() was a drop-in replacement for udelay()
where wakeup is flexible. But that's only true in non-atomic contexts,
where it's possible to sleep instead of delay.

Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
kernel/time/timer.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 3a95f97..c024c9f 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1702,9 +1702,15 @@ static void __sched do_usleep_range(unsigned long min, unsigned long max)

- * usleep_range - Drop in replacement for udelay where wakeup is flexible
+ * usleep_range - sleep for an approximate time
* @min: Minimum time in usecs to sleep
* @max: Maximum time in usecs to sleep
+ *
+ * In non-atomic context where the exact wakeup time is flexible, use
+ * usleep_range() instead of udelay(). The sleep improves responsiveness
+ * by avoiding the CPU-hogging busy-wait of udelay(), and the range reduces
+ * power usage by allowing hrtimers to take advantage of an already-
+ * scheduled interrupt instead of scheduling a new one just for this sleep.
void __sched usleep_range(unsigned long min, unsigned long max)