Re: Question about usage of RCU in the input layer

On Thu, 19 Mar 2009 00:23:56 -0700
Dmitry Torokhov [off-list ref] wrote:

Hi Arjan,

On Wednesday 18 March 2009 21:58:12 Arjan van de Ven wrote:

quoted

Hi,

the input layer does a "synchronize_rcu()" after a
list_add_tail_rcu(), which is costing me 1 second of boot time.....
And based on my understanding of the RCU concept, you only need to
synchronize on delete, not on addition... so I think the
synchronize is entirely redundant here...

It is there to guarantee that once we registered the handle all
subsequent input events will be delivered through it.

afaik rcu already guarantees that even without a synchronize;
the only reason you would need a synchronize is to guarantee that
people STOPPED using your memory. Or am I now totally misunderstanding
RCU ?