From: Simon Horman Date: Wed, 22 May 2013 05:50:31 +0000 (+0900) Subject: sched: add cond_resched_rcu() helper X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=f6f3c437d09e2f62533034e67bfb4385191e992c;p=deliverable%2Flinux.git sched: add cond_resched_rcu() helper This is intended for use in loops which read data protected by RCU and may have a large number of iterations. Such an example is dumping the list of connections known to IPVS: ip_vs_conn_array() and ip_vs_conn_seq_next(). The benefits are for CONFIG_PREEMPT_RCU=y where we save CPU cycles by moving rcu_read_lock and rcu_read_unlock out of large loops but still allowing the current task to be preempted after every loop iteration for the CONFIG_PREEMPT_RCU=n case. The call to cond_resched() is not needed when CONFIG_PREEMPT_RCU=y. Thanks to Paul E. McKenney for explaining this and for the final version that checks the context with CONFIG_DEBUG_ATOMIC_SLEEP=y for all possible configurations. The function can be empty in the CONFIG_PREEMPT_RCU case, rcu_read_lock and rcu_read_unlock are not needed in this case because the task can be preempted on indication from scheduler. Thanks to Peter Zijlstra for catching this and for his help in trying a solution that changes __might_sleep. Initial cond_resched_rcu_lock() function suggested by Eric Dumazet. Tested-by: Julian Anastasov Signed-off-by: Julian Anastasov Signed-off-by: Simon Horman Acked-by: Peter Zijlstra Signed-off-by: Pablo Neira Ayuso --- diff --git a/include/linux/sched.h b/include/linux/sched.h index 178a8d909f14..4ff8da189253 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2444,6 +2444,15 @@ extern int __cond_resched_softirq(void); __cond_resched_softirq(); \ }) +static inline void cond_resched_rcu(void) +{ +#if defined(CONFIG_DEBUG_ATOMIC_SLEEP) || !defined(CONFIG_PREEMPT_RCU) + rcu_read_unlock(); + cond_resched(); + rcu_read_lock(); +#endif +} + /* * Does a critical section need to be broken due to another * task waiting?: (technically does not depend on CONFIG_PREEMPT,