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authorBjorn Helgaas <bhelgaas@google.com>2016-05-31 16:23:02 -0500
committerThomas Gleixner <tglx@linutronix.de>2016-06-10 00:59:14 +0200
commitb5227d03b7191a9a44bf75a4c228a6a9ddbe781b (patch)
treec9598d40a1161ddaf9afef234f8c6c2c4bc5dcaa /kernel/time
parent2895a5e5b3ae78d9923a91fce405d4a2f32c4309 (diff)
downloadlinux-b5227d03b7191a9a44bf75a4c228a6a9ddbe781b.tar.bz2
timers: Clarify usleep_range() function comment
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@google.com> Cc: John Stultz <john.stultz@linaro.org> Link: http://lkml.kernel.org/r/20160531212302.28502.44995.stgit@bhelgaas-glaptop2.roam.corp.google.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/time')
-rw-r--r--kernel/time/timer.c8
1 files changed, 7 insertions, 1 deletions
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 3a95f9728778..67dd6103003a 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)
{