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Re: [Xen-devel] [PATCH v3 01/15] x86/IRQ: deal with move-in-progress state in fixup_irqs()


  • To: Jan Beulich <JBeulich@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Wed, 3 Jul 2019 16:39:14 +0100
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  • Cc: Wei Liu <wei.liu2@xxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
  • Delivery-date: Wed, 03 Jul 2019 15:39:45 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 17/05/2019 11:44, Jan Beulich wrote:
> The flag being set may prevent affinity changes, as these often imply
> assignment of a new vector. When there's no possible destination left
> for the IRQ, the clearing of the flag needs to happen right from
> fixup_irqs().
>
> Additionally _assign_irq_vector() needs to avoid setting the flag when
> there's no online CPU left in what gets put into ->arch.old_cpu_mask.
> The old vector can be released right away in this case.

This suggests that it is a bugfix, but it isn't clear what happens when
things go wrong.

> --- a/xen/arch/x86/irq.c
> +++ b/xen/arch/x86/irq.c
> @@ -2418,15 +2462,18 @@ void fixup_irqs(const cpumask_t *mask, b
>          if ( desc->handler->enable )
>              desc->handler->enable(desc);
>  
> +        cpumask_copy(&affinity, desc->affinity);
> +
>          spin_unlock(&desc->lock);
>  
>          if ( !verbose )
>              continue;
>  
> -        if ( break_affinity && set_affinity )
> -            printk("Broke affinity for irq %i\n", irq);
> -        else if ( !set_affinity )
> -            printk("Cannot set affinity for irq %i\n", irq);
> +        if ( !set_affinity )
> +            printk("Cannot set affinity for IRQ%u\n", irq);
> +        else if ( break_affinity )
> +            printk("Broke affinity for IRQ%u, new: %*pb\n",
> +                   irq, nr_cpu_ids, &affinity);

While I certainly prefer this version, I should point out that you
refused to accept my patches like this, and for consistency with the
rest of the codebase, you should be using cpumask_bits().

~Andrew

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