-- On Wed, 26 Sep 2007, Peter Zijlstra wrote: > > On Wed, 2007-09-26 at 12:55 -0700, Paul E. McKenney wrote: > > > Well, we could make spin_lock_irqsave() invoke rcu_read_lock() and > > spin_lock_irqrestore() invoke rcu_read_unlock(), with similar adjustments > > to the other primitives in this group. Then RCU priority boosting would > > kick in if configured. > > Might be me, but 'hiding' the RCU scope like that makes my skin crawl. > What is wrong with using rcu_read_lock() explicitly where you depend on > it? It even makes the code cleaner in that it documents the usage. > > These blanket locks like lock_kernel(), preempt_disable(), > local_irq_disable() etc. are very hard to get rid of because they don't > document what is protected. > > Please lets not add to this mess and keep all this explicit. > > Yes, -rt changes the preemption model, and that has concequences. But > IMHO the resulting code is cleaner in most cases. > > I'd go as far as to depricate synchronize_sched() and replace all its > users with proper RCU. > > The more I think of it, the more I dislike this synchronize_all_irqs() > and the 'magic' property of irq handlers. Thinking a little more about this, I fully agree with Peter. What code needs to know that all spin_locks have released, or you want to know all irq handlers are done? Seems that this is a broad data to ask for and will be a bitch to clean up when we find out that this is not scalable. This all sounds like reinventing the BKL. If you simply want a RCU type of scheme, then simply use RCU. I second deprecating "synchronize_sched". Everything that does RCU type locking (that is waiting for some kind of grace period to finish) should simply use RCU and not a "wait for all processes to voluntarily schedule" or "wait for all interrupt handlers to finish". -- Steve - To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
