If a non-nohz_full= CPU is non-idle, it will have a scheduling-clock interrupt, and therefore doesn't need the timekeeping CPU to keep its scheduling-clock interrupt going. This commit therefore ignores the idle state of non-nohz_full CPUs when determining whether or not the timekeeping CPU can safely turn off its scheduling-clock interrupt.
Signed-off-by: Paul E. McKenney <[email protected]> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index ddad959a9132..eaa32e4c228d 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2789,8 +2789,13 @@ static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq) * system-idle state. This means that the timekeeping CPU must * invoke rcu_sysidle_force_exit() directly if it does anything * more than take a scheduling-clock interrupt. + * + * In addition if we are not a nohz_full= CPU, then when we are + * non-idle we have our own tick, so we don't need the timekeeping + * CPU to keep a tick on our behalf. We assume that the timekeeping + * CPU is also a nohz_full= CPU. */ - if (smp_processor_id() == tick_do_timer_cpu) + if (!tick_nohz_full_cpu(smp_processor_id())) return; /* Update system-idle state: We are clearly no longer fully idle! */ @@ -2810,11 +2815,11 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, /* * If some other CPU has already reported non-idle, if this is - * not the flavor of RCU that tracks sysidle state, or if this - * is an offline or the timekeeping CPU, nothing to do. + * not the flavor of RCU that tracks sysidle state, or if this is + * an offline or !nohz_full= or the timekeeping CPU, nothing to do. */ if (!*isidle || rdp->rsp != rcu_sysidle_state || - cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu) + cpu_is_offline(rdp->cpu) || !tick_nohz_full_cpu(rdp->cpu)) return; if (rcu_gp_in_progress(rdp->rsp)) WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
