Re: [patch] big IRQ lock removal, 2.5.27-G0

Ingo Molnar (mingo@elte.hu)
Wed, 24 Jul 2002 09:19:15 +0200 (CEST)


On Wed, 24 Jul 2002, Oleg Nesterov wrote:

> > okay - i've fixed irq_exit() once more in -G4
>
> found G5, your forgot to add preempt_disable() in irq_exit()
>
> #define irq_exit()
> do {
> + preempt_disable();
> preempt_count() -= IRQ_EXIT_OFFSET;
> if (!in_interrupt() && softirq_pending(smp_processor_id()))
>
> Oleg.

nope, it's tricky, check out the define of IRQ_EXIT_OFFSET, it has the
plus 1 count added already.

using preempt_disable() has the problem of putting a barrier() between the
++ and the -IRQ_OFFSET, causing one more instruction to be generated.

but there was another (not too critical) bug here - irq_enter() needs to
have a barrier() after manipulating the preemption count, irq_exit() needs
to have a barrier() before. Fixed in my tree.

Ingo

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