On Thu, Jan 2, 2014 at 7:05 AM, Davidlohr Bueso <davidl...@hp.com> wrote: > > In futex_wake() there is clearly no point in taking the hb->lock if we know > beforehand that there are no tasks to be woken.
Btw, I think we could optimize this a bit further for the wakeup case. wake_futex() does a get_task_struct(p)/put_task_struct(p) around its actual waking logic, and I don't think that's necessary. The task structures are RCU-delayed, and the task cannot go away until the "q->lock_ptr = NULL" afaik, so you could replace that atomic inc/dec with just a RCU read region. Maybe it's not a big deal ("wake_up_state()" ends up getting the task struct pi_lock anyway, so it's not like we can avoid toucing the task structure), but I'm getting the feeling that we're doing a lot of unnecessary work here. This only triggers for the actual case of having a task to wake up, though, so not your particular test load. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/