[tip:sched/core] sched: Add a comment to get_cpu_idle_time_us()

[tip-bot for Arjan van de Ven]

Commit-ID:  b1f724c3055fa75a31d272222213647547a2d3d4
Gitweb:     http://git.kernel.org/tip/b1f724c3055fa75a31d272222213647547a2d3d4
Author:     Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
AuthorDate: Sun, 9 May 2010 08:22:08 -0700
Committer:  Ingo Molnar <mingo@xxxxxxx>
CommitDate: Sun, 9 May 2010 19:35:25 +0200

sched: Add a comment to get_cpu_idle_time_us()

The exported function get_cpu_idle_time_us() has no comment
describing it; add a kerneldoc comment

Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: davej@xxxxxxxxxx
LKML-Reference: <20100509082208.7cb721f0@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 kernel/time/tick-sched.c |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index f25735a..358822e 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -179,6 +179,20 @@ static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
 	return now;
 }
 
+/**
+ * get_cpu_idle_time_us - get the total idle time of a cpu
+ * @cpu: CPU number to query
+ * @last_update_time: variable to store update time in
+ *
+ * Return the cummulative idle time (since boot) for a given
+ * CPU, in microseconds. The idle time returned includes
+ * the iowait time (unlike what "top" and co report).
+ *
+ * This time is measured via accounting rather than sampling,
+ * and is as accurate as ktime_get() is.
+ *
+ * This function returns -1 if NOHZ is not enabled.
+ */
 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
 {
 	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
--
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