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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v1b 1/9] x86/IRQ: deal with move-in-progress state in fixup_irqs()
On Mon, Apr 29, 2019 at 09:40:14AM -0600, 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.
>
> Also extend the log message about broken affinity to include the new
> affinity as well, allowing to notice issues with affinity changes not
> actually having taken place. Swap the if/else-if order there at the
> same time to reduce the amount of conditions checked.
>
> At the same time replace two open coded instances of the new helper
> function.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v2: Also update vector_irq[] in the code added to fixup_irqs().
>
> --- unstable.orig/xen/arch/x86/irq.c 2019-04-29 17:34:16.726542659 +0200
> +++ unstable/xen/arch/x86/irq.c 2019-04-29 15:05:39.000000000 +0200
> @@ -242,6 +242,20 @@ void destroy_irq(unsigned int irq)
> xfree(action);
> }
>
> +static void release_old_vec(struct irq_desc *desc)
> +{
> + unsigned int vector = desc->arch.old_vector;
> +
> + desc->arch.old_vector = IRQ_VECTOR_UNASSIGNED;
> + cpumask_clear(desc->arch.old_cpu_mask);
> +
> + if ( desc->arch.used_vectors )
Wouldn't it be better to clean the bitmap when vector !=
IRQ_VECTOR_UNASSIGNED?
I haven't checked all the callers, but I don't think it's valid to
call release_old_vec with desc->arch.old_vector ==
IRQ_VECTOR_UNASSIGNED, in which case I would add an ASSERT.
> + {
> + ASSERT(test_bit(vector, desc->arch.used_vectors));
> + clear_bit(vector, desc->arch.used_vectors);
> + }
> +}
> +
> static void __clear_irq_vector(int irq)
> {
> int cpu, vector, old_vector;
> @@ -285,14 +299,7 @@ static void __clear_irq_vector(int irq)
Kind of unrelated, but I think the check at the top of
__clear_irq_vector should be:
BUG_ON(desc->arch.vector == IRQ_VECTOR_UNASSIGNED);
Rather than the current:
BUG_ON(!desc->arch.vector);
There's a lot of logic that would go extremely wrong if vector is -1.
> per_cpu(vector_irq, cpu)[old_vector] = ~irq;
> }
>
> - desc->arch.old_vector = IRQ_VECTOR_UNASSIGNED;
> - cpumask_clear(desc->arch.old_cpu_mask);
> -
> - if ( desc->arch.used_vectors )
> - {
> - ASSERT(test_bit(old_vector, desc->arch.used_vectors));
> - clear_bit(old_vector, desc->arch.used_vectors);
> - }
> + release_old_vec(desc);
>
> desc->arch.move_in_progress = 0;
While there it might be nice to convert move_in_progress to a boolean.
> }
> @@ -517,12 +524,21 @@ next:
> /* Found one! */
> current_vector = vector;
> current_offset = offset;
> - if (old_vector > 0) {
> - desc->arch.move_in_progress = 1;
> - cpumask_copy(desc->arch.old_cpu_mask, desc->arch.cpu_mask);
> +
> + if ( old_vector > 0 )
> + {
> + cpumask_and(desc->arch.old_cpu_mask, desc->arch.cpu_mask,
> + &cpu_online_map);
> desc->arch.old_vector = desc->arch.vector;
> + if ( !cpumask_empty(desc->arch.old_cpu_mask) )
> + desc->arch.move_in_progress = 1;
> + else
> + /* This can happen while offlining a CPU. */
> + release_old_vec(desc);
> }
> +
> trace_irq_mask(TRC_HW_IRQ_ASSIGN_VECTOR, irq, vector, &tmp_mask);
> +
> for_each_cpu(new_cpu, &tmp_mask)
> per_cpu(vector_irq, new_cpu)[vector] = irq;
> desc->arch.vector = vector;
> @@ -691,14 +707,8 @@ void irq_move_cleanup_interrupt(struct c
>
> if ( desc->arch.move_cleanup_count == 0 )
> {
> - desc->arch.old_vector = IRQ_VECTOR_UNASSIGNED;
> - cpumask_clear(desc->arch.old_cpu_mask);
> -
> - if ( desc->arch.used_vectors )
> - {
> - ASSERT(test_bit(vector, desc->arch.used_vectors));
> - clear_bit(vector, desc->arch.used_vectors);
> - }
> + ASSERT(vector == desc->arch.old_vector);
> + release_old_vec(desc);
> }
> unlock:
> spin_unlock(&desc->lock);
> @@ -2391,6 +2401,33 @@ void fixup_irqs(const cpumask_t *mask, b
> continue;
> }
>
> + /*
> + * In order for the affinity adjustment below to be successful, we
> + * need __assign_irq_vector() to succeed. This in particular means
> + * clearing desc->arch.move_in_progress if this would otherwise
> + * prevent the function from succeeding. Since there's no way for the
> + * flag to get cleared anymore when there's no possible destination
> + * left (the only possibility then would be the IRQs enabled window
> + * after this loop), there's then also no race with us doing it here.
> + *
> + * Therefore the logic here and there need to remain in sync.
> + */
> + if ( desc->arch.move_in_progress &&
> + !cpumask_intersects(mask, desc->arch.cpu_mask) )
> + {
> + unsigned int cpu;
> +
> + cpumask_and(&affinity, desc->arch.old_cpu_mask, &cpu_online_map);
> +
> + spin_lock(&vector_lock);
> + for_each_cpu(cpu, &affinity)
> + per_cpu(vector_irq, cpu)[desc->arch.old_vector] = ~irq;
> + spin_unlock(&vector_lock);
> +
> + release_old_vec(desc);
> + desc->arch.move_in_progress = 0;
> + }
> +
> cpumask_and(&affinity, &affinity, mask);
> if ( cpumask_empty(&affinity) )
> {
> @@ -2409,15 +2446,18 @@ 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);
I guess it's fine to have those without rate-limiting because
fixup_irqs is only called for admin-triggered actions, so there's no
risk of console flooding.
Thanks, Roger.
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