[PATCH] nohz: Fix ondemand governor not always ramping up on 100% load.

[PATCH] nohz: Fix ondemand governor not always ramping up on 100% load.

[Arve Hjønnevåg]

On systems that perform the context switch with interrupts enabled
(e.g. ARM) get_cpu_idle_time_us could get stuck returning the last
idle time when the cpu is busy. If an interrupt occurs while
switching to the idle thread, and this interrupt wakes up a thread,
need-resched will be set on the idle thread, but since we have not
finished switching to the idle thread tick_nohz_stop_sched_tick will
be called. (idle_cpu is true since the head of the runqueue is the
idle thread, but need_resched returns false since we are still
running in the context of the old thread)

Fix this by not calling tick_nohz_start_idle when returning from an
interrupt while the idle thread is in its schedule phase.
(!ts->inidle)

Signed-off-by: Arve Hjønnevåg <arve@android.com>
---
 kernel/time/tick-sched.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index d3f1ef4..4012da6 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -222,7 +222,6 @@ void tick_nohz_stop_sched_tick(int inidle)
 
 	cpu = smp_processor_id();
 	ts = &per_cpu(tick_cpu_sched, cpu);
-	now = tick_nohz_start_idle(ts);
 
 	/*
 	 * If this cpu is offline and it is the one which updates
@@ -242,6 +241,7 @@ void tick_nohz_stop_sched_tick(int inidle)
 	if (!inidle && !ts->inidle)
 		goto end;
 
+	now = tick_nohz_start_idle(ts);
 	ts->inidle = 1;
 
 	if (need_resched())
-- 
1.6.1