On Wed, 25 Sep 2013 06:32:10 +0200 Mario Kleiner <mario.kleiner@xxxxxxxxxxxxxxxx> wrote: > I assume if a spin_lock_irqsave doesn't really disable interrupts on a > RT kernel with normal spinlocks then local_irq_disable won't really > disable interrupts either? > That is incorrect. On PREEMPT_RT, you are right about spin_lock_irqsave() not disabling interrupts, but local_irq_disable() does indeed disable interrupts. Open coded local_irq_disable() usually ends up being a bug as it does nothing to synchronize interrupts from other CPUs. But most of those bugs have been removed, and there are some very legit reasons for using local_irq_disable(). PREEMPT_RT honors those. The reason PREEMPT_RT does not disable interrupts for spin_lock_irqsave(), is because that's usually used for when a interrupt uses the same spinlock. You need the irqsave() part in order to prevent a deadlock, if the code that has the spinlock gets preempted by the interrupt and that interrupt tries to grab the same lock. Because PREEMPT_RT runs interrupts as threads, we don't have that issue, because if the interrupt preempts the holder of the lock and it tries to grab the same lock, it will just block like any other thread trying to grab that lock. That is, spinlocks turn into mutexes on PREEMPT_RT. -- Steve _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
