An idle cpu enters cpu_idle_poll() if it is set in the
tick_broadcast_force_mask.
This is so that it does not incur the overhead of entering idle states when it
is expected
to be woken up anytime then through a broadcast IPI. The condition that forces
an exit out
of the idle polling is the check on setting of the TIF_NEED_RESCHED flag for
the idle thread.
When the broadcast IPI does arrive, it is not guarenteed that the handler sets
the
TIF_NEED_RESCHED flag. Hence although the cpu is cleared in the
tick_broadcast_force_mask,
it continues to loop in cpu_idle_poll unnecessarily wasting power. Hence exit
the idle
poll loop if the tick_broadcast_force_mask gets cleared and enter idle states.
Of course if the cpu has entered cpu_idle_poll() on being asked to poll
explicitly,
it continues to poll till it is asked to reschedule.
Signed-off-by: Preeti U Murthy <pre...@linux.vnet.ibm.com>
---
kernel/sched/idle.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index c47fce7..aaf1c1d 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -47,7 +47,8 @@ static inline int cpu_idle_poll(void)
rcu_idle_enter();
trace_cpu_idle_rcuidle(0, smp_processor_id());
local_irq_enable();
- while (!tif_need_resched())
+ while (!tif_need_resched() &&
+ (cpu_idle_force_poll || tick_check_broadcast_expired()))
cpu_relax();
trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
rcu_idle_exit();
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