On Thu, 19 Mar 2009 14:26:28 +0530 Dipankar Sarma <dipankar@xxxxxxxxxx> wrote: > 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() ? one cpu is doing a lot of i2c traffic which is a bunch of udelay()s in loops.. then it does quite a bit of uncached memory access, and the lot takes quite while. > What driver is this ? How early > in the boot is this happening ? during kernel boot. I suppose my question is also more generic.. why synchronize when it's not needed? At least based on my understanding of RCU (but you're the expert), you don't need to synchronize for an add, only between a delete and a (k)free..... -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
