Messages in this thread Patch in this message | | | Subject | [PATCH] idle/tick-broadcast: Exit cpu idle poll loop when cleared from tick_broadcast_force_mask | From | Preeti U Murthy <> | Date | Mon, 19 Jan 2015 10:57:54 +0530 |
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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 <preeti@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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