On Wed, Mar 18, 2009 at 09:58:12PM -0700, Arjan van de Ven wrote:

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...

The more appropriate question is - why is synchronize_rcu() taking
1 second ? Any idea what the other CPUs are doing at the time
of calling synchronize_rcu() ? What driver is this ? How early
in the boot is this happening ? 

Thanks
Dipankar