Messages in this thread | | | Subject | Re: [patch 01/17] RCU read sched | From | Peter Zijlstra <> | Date | Sat, 02 Aug 2008 01:04:29 +0200 |
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On Fri, 2008-08-01 at 14:10 -0700, Paul E. McKenney wrote: > On Tue, Jul 15, 2008 at 06:26:05PM -0400, Mathieu Desnoyers wrote: > > Add rcu_read_lock_sched() and rcu_read_unlock_sched() to rcupdate.h to match the > > recently added write-side call_rcu_sched() and rcu_barrier_sched(). They also > > match the no-so-recently-added synchronize_sched(). > > > > It will help following matching use of the update/read lock primitives. Those > > new read lock will replace preempt_disable()/enable() used in pair with > > RCU-classic synchronization. > > Looks good, but... > > synchronize_sched(), call_rcu_sched(), and rcu_barrier_sched() can also > pair up with: > > o local_irq_save() and local_irq_restore() > o local_irq_disable() and local_irq_enable()
> o spin_lock_irqsave() and spin_lock_irqrestore()
You can't actually, as on PREEMP_RT these will not actuall disable preemption.
> o etc. etc. > > I do very much like the idea of marking the intent of matching with > RCU, but am getting a bit queasy about adding rcu_read_lock_sched_irq() > and so on.
I'm thinking that if you disable interrupts, you're doing that for another reason than RCU, so I'm not seeing the need for rcu_read_lock_sched_irq variants.
Also, we should be very careful with using the *sched* RCU variant as it really relies on disabling preemption - we should only use it when there really is no other option, as we generally prefer to keep stuff preemptable.
> Thoughts? Other than having an rcu_read_lock_sched_nop() or some > other window-dressing macro that doesn't really do anything? (Which > might really be the right thing to do...)
Afraid you lost me here..
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