linux-kernel - Re: "irq 4: Affinity broken due to vector space exhaustion." warning on restart of ttyS0 console

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Date:   Wed, 09 Dec 2020 19:28:49 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Shung-Hsi Yu <shung-hsi.yu@...e.com>
Cc:     Prarit Bhargava <prarit@...hat.com>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Marc Zyngier <maz@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Ming Lei <ming.lei@...hat.com>, Peter Xu <peterx@...hat.com>
Subject: Re: "irq 4: Affinity broken due to vector space exhaustion." warning on restart of ttyS0 console

Hi Shung-Hsi!

On Wed, Dec 09 2020 at 14:33, Shung-Hsi Yu wrote:
> On Tue, Nov 10, 2020 at 09:56:27PM +0100, Thomas Gleixner wrote:
>> The real problem is irqbalanced aggressively exhausting the vector space
>> of a _whole_ socket to the point that there is not a single vector left
>> for serial. That's the problem you want to fix.
>
> I believe this warning also gets triggered even when there's _no_ vector
> exhaustion.
>
> This seem to happen when the IRQ's affinity mask is set (wrongly) to CPUs on
> a different NUMA node (e.g. cpumask_of_node(1) when the irqd->irq == 0).
>
>   $ lscpu
>   ...
>   NUMA node0 CPU(s):   0-25,52-77
>   NUMA node1 CPU(s):   26-51,78-103
>
>   $ cat /sys/kernel/debug/tracing/trace
>            ...
>     (agetty)-3004    [047] d...    81.777152: vector_activate: irq=4 is_managed=0 can_reserve=1 reserve=0
>     (agetty)-3004    [047] d...    81.777157: vector_alloc: irq=4 vector=0 reserved=1 ret=-22
>     ----------------------------------------> irq_matrix_alloc() failed with
>                                               EINVAL because the cpumask
>                                               passed in is empty, which is a
>                                               result of affmask being
>                                               (ff,ffffc000,000fffff,fc000000)
>                                               and cpumask_of_node(node)
>                                               being
>                                               (00,00003fff,fff00000,03ffffff). 
>
>     (agetty)-3004    [047] d...    81.789349: irq_matrix_alloc: bit=33 cpu=1 online=1 avl=199 alloc=2 managed=1 online_maps=104 global_avl=20688, global_rsvd=341, total_alloc=216
>     (agetty)-3004    [047] d...    81.789351: vector_alloc: irq=4 vector=33 reserved=1 ret=0
>     (agetty)-3004    [047] d...    81.789353: vector_update: irq=4 vector=33 cpu=1 prev_vector=0 prev_cpu=26
>     (agetty)-3004    [047] d...    81.789355: vector_config: irq=4 vector=33 cpu=1 apicdest=0x00000002
>     ----------------------------------------> "irq 4: Affinity broken due to
>                                               vector space exhaustion."
>                                               warning shows up
>

Ok. That's a different story. Nice explanation!

But the fix is not to tone down the warning. The proper fix is to do the
search in the correct order.

Thanks,

        tglx
---
 arch/x86/kernel/apic/vector.c |   24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

--- a/arch/x86/kernel/apic/vector.c
+++ b/arch/x86/kernel/apic/vector.c
@@ -273,20 +273,24 @@ static int assign_irq_vector_any_locked(
 	const struct cpumask *affmsk = irq_data_get_affinity_mask(irqd);
 	int node = irq_data_get_node(irqd);
 
-	if (node == NUMA_NO_NODE)
-		goto all;
-	/* Try the intersection of @affmsk and node mask */
-	cpumask_and(vector_searchmask, cpumask_of_node(node), affmsk);
-	if (!assign_vector_locked(irqd, vector_searchmask))
-		return 0;
-	/* Try the node mask */
-	if (!assign_vector_locked(irqd, cpumask_of_node(node)))
-		return 0;
-all:
+	if (node != NUMA_NO_NODE) {
+		/* Try the intersection of @affmsk and node mask */
+		cpumask_and(vector_searchmask, cpumask_of_node(node), affmsk);
+		if (!assign_vector_locked(irqd, vector_searchmask))
+			return 0;
+	}
+
 	/* Try the full affinity mask */
 	cpumask_and(vector_searchmask, affmsk, cpu_online_mask);
 	if (!assign_vector_locked(irqd, vector_searchmask))
 		return 0;
+
+	if (node != NUMA_NO_NODE) {
+		/* Try the node mask */
+		if (!assign_vector_locked(irqd, cpumask_of_node(node)))
+			return 0;
+	}
+
 	/* Try the full online mask */
 	return assign_vector_locked(irqd, cpu_online_mask);
 }