From ac1bea85781e9004da9b3e8a4b097c18492d857c Mon Sep 17 00:00:00 2001 From: Paul E. McKenney Date: Sun, 16 Mar 2014 21:36:25 -0700 Subject: sched,rcu: Make cond_resched() report RCU quiescent states Given a CPU running a loop containing cond_resched(), with no other tasks runnable on that CPU, RCU will eventually report RCU CPU stall warnings due to lack of quiescent states. Fortunately, every call to cond_resched() is a perfectly good quiescent state. Unfortunately, invoking rcu_note_context_switch() is a bit heavyweight for cond_resched(), especially given the need to disable preemption, and, for RCU-preempt, interrupts as well. This commit therefore maintains a per-CPU counter that causes cond_resched(), cond_resched_lock(), and cond_resched_softirq() to call rcu_note_context_switch(), but only about once per 256 invocations. This ratio was chosen in keeping with the relative time constants of RCU grace periods. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/sched/core.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'kernel/sched') diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 268a45ea238c..9f530c9ed911 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4051,6 +4051,7 @@ static void __cond_resched(void) int __sched _cond_resched(void) { + rcu_cond_resched(); if (should_resched()) { __cond_resched(); return 1; @@ -4069,15 +4070,18 @@ EXPORT_SYMBOL(_cond_resched); */ int __cond_resched_lock(spinlock_t *lock) { + bool need_rcu_resched = rcu_should_resched(); int resched = should_resched(); int ret = 0; lockdep_assert_held(lock); - if (spin_needbreak(lock) || resched) { + if (spin_needbreak(lock) || resched || need_rcu_resched) { spin_unlock(lock); if (resched) __cond_resched(); + else if (unlikely(need_rcu_resched)) + rcu_resched(); else cpu_relax(); ret = 1; @@ -4091,6 +4095,7 @@ int __sched __cond_resched_softirq(void) { BUG_ON(!in_softirq()); + rcu_cond_resched(); /* BH disabled OK, just recording QSes. */ if (should_resched()) { local_bh_enable(); __cond_resched(); -- cgit v1.2.3