On 20/10/21 12:02, Wanpeng Li wrote:
+#ifdef CONFIG_PREEMPT_RCU + /* The cost of rcu_read_lock() is nontrivial for preemptable RCU. */ + if (!rcuwait_active(w)) + return ret; +#endif + + rcu_read_lock(); + task = rcu_dereference(w->task); if (task) ret = wake_up_process(task); (If you don't, rcu_read_lock is essentially preempt_disable() and it should not have a large overhead). You still need the memory barrier though, in order to avoid missed wakeups; shameless plug for my article athttps://lwn.net/Articles/847481/.You are right, the cost of rcu_read_lock() for preemptable RCU introduces too much overhead, do you want to send a separate patch?
Yes, I'll take care of this. Thanks! Paolo
