| Message ID | 20150121105655.15279.59626.stgit@preeti.in.ibm.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Michael Ellerman |
| Headers | show |
On Wed, 21 Jan 2015, Preeti U Murthy wrote: > cpu_idle_poll() is entered into when either the cpu_idle_force_poll is set or > tick_check_broadcast_expired() returns true. The exit condition from > cpu_idle_poll() is tif_need_resched(). > > However this does not take into account scenarios where cpu_idle_force_poll > changes or tick_check_broadcast_expired() returns false, without setting > the resched flag. So a cpu will be caught in cpu_idle_poll() needlessly, > thereby wasting power. Add an explicit check on cpu_idle_force_poll and > tick_check_broadcast_expired() to the exit condition of cpu_idle_poll() > to avoid this. > > Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> > --- > Changes from V1: Modified the Changelog > > 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(); > >
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();
cpu_idle_poll() is entered into when either the cpu_idle_force_poll is set or tick_check_broadcast_expired() returns true. The exit condition from cpu_idle_poll() is tif_need_resched(). However this does not take into account scenarios where cpu_idle_force_poll changes or tick_check_broadcast_expired() returns false, without setting the resched flag. So a cpu will be caught in cpu_idle_poll() needlessly, thereby wasting power. Add an explicit check on cpu_idle_force_poll and tick_check_broadcast_expired() to the exit condition of cpu_idle_poll() to avoid this. Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com> --- Changes from V1: Modified the Changelog kernel/sched/idle.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)