linux-kernel - Re: [PATCH] irqchip/armada-370-xp: Enable MSI affinity configuration

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Date:   Thu, 21 Apr 2022 14:00:27 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Nathan Rossi <nathan@...hanrossi.com>
Cc:     Marc Zyngier <maz@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Nathan Rossi <nathan.rossi@...i.com>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] irqchip/armada-370-xp: Enable MSI affinity configuration

> > >  static void armada_370_xp_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
> > >  {
> > > +#ifdef CONFIG_SMP
> > > +     unsigned int cpu = cpumask_first(irq_data_get_effective_affinity_mask(data));
> > > +
> > > +     msg->data = (1 << (cpu + 8)) | (data->hwirq + PCI_MSI_DOORBELL_START);
> >
> > BIT(cpu + 8) | ...
> >
> > > +#else
> > > +     msg->data = 0xf00 | (data->hwirq + PCI_MSI_DOORBELL_START);
> >
> > This paints the existing code a bit differently. This seems to target
> > all 4 CPUs. Why is that? I'd expect only bit 8 to be set, and the
> > whole #ifdefery to go away.
> 
> I will remove the #ifdef in a v2 patch that addresses your
> other comments.

Please try to remove all the #ifdef'ery.

> > >  static int armada_370_xp_msi_set_affinity(struct irq_data *irq_data,
> > >                                         const struct cpumask *mask, bool force)
> > >  {
> > > -      return -EINVAL;
> > > +#ifdef CONFIG_SMP
> > > +     unsigned int cpu;
> > > +
> > > +     if (!force)
> > > +             cpu = cpumask_any_and(mask, cpu_online_mask);
> > > +     else
> > > +             cpu = cpumask_first(mask);
> > > +
> > > +     if (cpu >= nr_cpu_ids)
> > > +             return -EINVAL;
> > > +
> > > +     irq_data_update_effective_affinity(irq_data, cpumask_of(cpu));
> > > +
> > > +     return IRQ_SET_MASK_OK;
> > > +#else
> > > +     return -EINVAL;
> > > +#endif

A quick look in cpumask.h suggests that if NR_CPUS == 1, there are
stub functions which return constant values. So you might not need
this #ifdef. However, i'm a network guy, not a scheduling guy, so
don't trust what i say...

     Andrew