On 01/20/2015 04:51 PM, Thomas Gleixner wrote: > On Mon, 19 Jan 2015, Preeti U Murthy wrote: >> 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())) > > You explain the tick_check_broadcast_expired() bit, but what about the > cpu_idle_force_poll part?
The last few lines which say "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" explains the cpu_idle_force_poll part. Perhaps I should s/poll explicitly/do cpu_idle_force_poll ? Regards Preeti U Murthy > > Thanks, > > tglx > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev