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SubjectRe: [PATCH] powerpc/irq: Run softirqs off the top of the irq stack
Hi Ben,

On Mon, 23 Sep 2013 14:35:58 +1000 Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:
>
> diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
> index c69440c..0c9646f 100644
> --- a/arch/powerpc/kernel/irq.c
> +++ b/arch/powerpc/kernel/irq.c
> @@ -443,46 +443,7 @@ void migrate_irqs(void)
>
> static inline void handle_one_irq(unsigned int irq)
> {
> - struct thread_info *curtp, *irqtp;
> - unsigned long saved_sp_limit;
> - struct irq_desc *desc;
> -
> - desc = irq_to_desc(irq);
> - if (!desc)
> - return;
> -
> - /* Switch to the irq stack to handle this */
> - curtp = current_thread_info();
> - irqtp = hardirq_ctx[smp_processor_id()];
> -
> - if (curtp == irqtp) {
> - /* We're already on the irq stack, just handle it */
> - desc->handle_irq(irq, desc);
> - return;
> - }
> -
> - saved_sp_limit = current->thread.ksp_limit;
> -
> - irqtp->task = curtp->task;
> - irqtp->flags = 0;
> -
> - /* Copy the softirq bits in preempt_count so that the
> - * softirq checks work in the hardirq context. */
> - irqtp->preempt_count = (irqtp->preempt_count & ~SOFTIRQ_MASK) |
> - (curtp->preempt_count & SOFTIRQ_MASK);
>
> - current->thread.ksp_limit = (unsigned long)irqtp +
> - _ALIGN_UP(sizeof(struct thread_info), 16);
> -
> - call_handle_irq(irq, desc, irqtp, desc->handle_irq);
> - current->thread.ksp_limit = saved_sp_limit;
> - irqtp->task = NULL;
> -
> - /* Set any flag that may have been set on the
> - * alternate stack
> - */
> - if (irqtp->flags)
> - set_bits(irqtp->flags, &curtp->flags);
> }

This function ends up as a single blank line ...

> @@ -519,18 +480,64 @@ void do_IRQ(struct pt_regs *regs)
> */
> irq = ppc_md.get_irq();
>
> - /* We can hard enable interrupts now */
> + /* We can hard enable interrupts now to allow perf interrupts */
> may_hard_irq_enable();
>
> /* And finally process it */
> - if (irq != NO_IRQ)
> - handle_one_irq(irq);

then you remove the only call, so why not just remove the function
completely?

--
Cheers,
Stephen Rothwell sfr@canb.auug.org.au
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