From 803b0ebae921714d1c36f0996db8125eda5fae53 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 23 Aug 2012 08:34:07 -0700 Subject: [PATCH] time: RCU permitted to stop idle entry via softirq The can_stop_idle_tick() function complains if a softirq vector is raised too late in the idle-entry process, presumably in order to prevent dangling softirq invocations from being delayed across the full idle period, which might be indefinitely long -- and if softirq was asserted any later than the call to this function, such a delay might well happen. However, RCU needs to be able to use softirq to stop idle entry in order to be able to drain RCU callbacks from the current CPU, which in turn enables faster entry into dyntick-idle mode, which in turn reduces power consumption. Because RCU takes this action at a well-defined point in the idle-entry path, it is safe for RCU to take this approach. This commit therefore silences the error message that is sometimes produced when the going-idle CPU suddenly finds that it has an RCU_SOFTIRQ to process. The error message will continue to be issued for other softirq vectors. Reported-by: Sedat Dilek Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Tested-by: Sedat Dilek Reviewed-by: Josh Triplett --- include/linux/interrupt.h | 2 ++ kernel/time/tick-sched.c | 3 ++- 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h index c5f856a040b9..5e4e6170f43a 100644 --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -430,6 +430,8 @@ enum NR_SOFTIRQS }; +#define SOFTIRQ_STOP_IDLE_MASK (~(1 << RCU_SOFTIRQ)) + /* map softirq index to softirq name. update 'softirq_to_name' in * kernel/softirq.c when adding a new softirq. */ diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 024540f97f74..4b1785a7bb83 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -436,7 +436,8 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) if (unlikely(local_softirq_pending() && cpu_online(cpu))) { static int ratelimit; - if (ratelimit < 10) { + if (ratelimit < 10 && + (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n", (unsigned int) local_softirq_pending()); ratelimit++;