linux-kernel - Re: pci_msix_alloc_irq

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Message-ID: <87ttgcuuvi.ffs@tglx>
Date: Fri, 26 Jul 2024 15:48:33 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Shay Drori <shayd@...dia.com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: pci_msix_alloc_irq_at() affinity

On Thu, Jul 25 2024 at 08:34, Shay Drori wrote:
> I did some testing with pci_msix_alloc_irq_at() and I noticed that the
> affinity provided, via “struct irq_affinity_desc *af_desc”, doesn’t have
> any affect.
>
> After some digging, I found out that irq_setup_affinity(), which is
> called by request_irq(), is setting the affinity as all the CPUs online,
> ignoring the affinity provided in pci_msix_alloc_irq_at().
> Is this on purpose or a bug?

It's an oversight. So far this has only been used with managed
interrupts and the non-managed parts at the beginning or end of the
interrupt group have been assigned the default affinity which makes this
obviously a non-problem because the startup code uses the default
affinity too.

> P.S. The bellow diff honors the affinity provided in
> pci_msix_alloc_irq_at()
>
> --- a/kernel/irq/irqdesc.c
> +++ b/kernel/irq/irqdesc.c
> @@ -530,6 +530,7 @@ static int alloc_descs(unsigned int start, unsigned 
> int cnt, int node,
>                                  flags = IRQD_AFFINITY_MANAGED |
>                                          IRQD_MANAGED_SHUTDOWN;
>                          }
> +                 flags |= IRQD_AFFINITY_SET;
>                          mask = &affinity->mask;
>                          node = cpu_to_node(cpumask_first(mask));
>                          affinity++;

Looks about right, though the diff is whitespace damaged.

Care to submit a proper patch?

Thanks,

        tglx