Re: [PATCH v2 04/17] ARM: Allow IPIs to be handled as normal interrupts

[Marc Zyngier]

On 2020-06-25 19:25, Valentin Schneider wrote:
> On 24/06/20 20:57, Marc Zyngier wrote:
> > @@ -696,9 +696,76 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
> >
> >       if ((unsigned)ipinr < NR_IPI)
> >               trace_ipi_exit_rcuidle(ipi_types[ipinr]);
> > +}
> > +
> > +/* Legacy version, should go away once all irqchips have been 
> > converted */
> > +void handle_IPI(int ipinr, struct pt_regs *regs)
> > +{
> > +	struct pt_regs *old_regs = set_irq_regs(regs);
> > +
> > +	irq_enter();
> > +	do_handle_IPI(ipinr);
> > +	irq_exit();
> > +
> >       set_irq_regs(old_regs);
> >  }
> >
> > +static irqreturn_t ipi_handler(int irq, void *data)
> > +{
> > +	do_handle_IPI(irq - ipi_irq_base);
> > +	return IRQ_HANDLED;
> > +}
> > +
> > +static void ipi_send(const struct cpumask *target, unsigned int ipi)
> > +{
> > +	__ipi_send_mask(ipi_desc[ipi], target);
> > +}
> > +
> > +static void ipi_setup(int cpu)
> > +{
> > +	if (ipi_irq_base) {
> > +		int i;
> > +
> > +		for (i = 0; i < nr_ipi; i++)
> > +			enable_percpu_irq(ipi_irq_base + i, 0);
> > +	}
> > +}
> > +
> > +static void ipi_teardown(int cpu)
> > +{
> > +	if (ipi_irq_base) {
> > +		int i;
> > +
> > +		for (i = 0; i < nr_ipi; i++)
> > +			disable_percpu_irq(ipi_irq_base + i);
> > +	}
> > +}
> > +
> > +void __init set_smp_ipi_range(int ipi_base, int n)
> > +{
> > +	int i;
> > +
> > +	WARN_ON(n < MAX_IPI);
> > +	nr_ipi = min(n, MAX_IPI);
>
>
> I got confused by that backtrace thing and NR_IPI vs MAX_IPI.
> I think I got it now : we don't want to call trace_ipi_raise() for
> IPI_CPU_BACKTRACE *but* we still need to alloc the desc and route it
> through the generic IPI layers.

Indeed, and I didn't want to have a bizarre "+ 1" hanging about.

> The only difference I can tell is that now we will get some trace 
> events
> for it via the handler entry/exit tracepoints - that shouldn't cause 
> any
> issue.

I hope so. I don't see how you can avoid all tracepoints anyway (if that
was the intention).

Thanks,

        M.
--
Jazz is not dead. It just smells funny...