2012/12/3 Vincent Guittot vincent.guittot@linaro.org:
With the coupled cpuidle driver (but probably also with other drivers), a CPU loops in a temporary safe state while waiting for other CPUs of its cluster to be ready to enter the coupled C-state. If an IRQ or a softirq occurs, the CPU will stay in this internal loop if there is no need to resched. The SCHED softirq clears the NOHZ and increases nr_busy_cpus. If there is no need to resched, we will not call set_cpu_sd_state_idle because of this internal loop in a cpuidle state. We have to call set_cpu_sd_state_idle in tick_nohz_irq_exit which is used to handle such situation.
I'm a bit confused with this.
set_cpu_sd_state_busy() is only called from nohz_kick_needed(). And it checks idle_cpu() before doing anything. So if no task is going to be scheduled, idle_cpu() prevents from calling set_cpu_sd_state_busy().
I'm probably missing something.
Thanks.
Signed-off-by: Vincent Guittot vincent.guittot@linaro.org
kernel/time/tick-sched.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 955d35b..b8d74ea 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -570,6 +570,8 @@ void tick_nohz_irq_exit(void) if (!ts->inidle) return;
set_cpu_sd_state_idle();/* Cancel the timer because CPU already waken up from the C-states*/ menu_hrtimer_cancel(); __tick_nohz_idle_enter(ts);-- 1.7.9.5
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