[PATCH] timers.c: document meaning of deferrable timer

[J. Bruce Fields]

From: J. Bruce Fields <bfields@xxxxxxxxxxxxxx>

Steal some text from 6e453a67510 "Add support for deferrable timers".
A reader shouldn't have to dig through the git logs for the basic
description of a deferrable timer.

Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxxxxxx>
---
 kernel/timer.c |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/timer.c b/kernel/timer.c
index ee305c8..947bcf6 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -90,8 +90,13 @@ static DEFINE_PER_CPU(struct tvec_base *, tvec_bases) = &boot_tvec_bases;
 
 /*
  * Note that all tvec_bases are 2 byte aligned and lower bit of
- * base in timer_list is guaranteed to be zero. Use the LSB for
- * the new flag to indicate whether the timer is deferrable
+ * base in timer_list is guaranteed to be zero. Use the LSB to
+ * indicate whether the timer is deferrable.
+ *
+ * A deferrable timer will work normally when the system is busy, but
+ * will not cause a CPU to come out of idle just to service it; instead,
+ * the timer will be serviced when the CPU eventually wakes up with a
+ * subsequent non-deferrable timer.
  */
 #define TBASE_DEFERRABLE_FLAG		(0x1)
 
-- 
1.7.0.4

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