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.
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 a402608..e19bbc9 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -526,6 +526,8 @@ void tick_nohz_irq_exit(void) if (!ts->inidle) return;
+ set_cpu_sd_state_idle(); + __tick_nohz_idle_enter(ts); }