Re: [PATCH] rcuwait: do not enter RCU protection unless a wakeup is needed

[Paolo Bonzini]

On 20/10/21 13:17, Peter Zijlstra wrote:
> AFAICT, rcu_read_lock() for PREEMPT_RCU is:
>
>    WRITE_ONCE(current->rcu_read_lock_nesting, READ_ONCE(current->rcu_read_lock_nesting) + 1);
>    barrier();

rcu_read_unlock() is the expensive one if you need to go down 
rcu_read_unlock_special().

Paolo

> Paul?