linux-kernel - [PATCH v1 1/1] irqchip/gic-v3-its: fixup IRQ affinities to account for online CPUs

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Message-Id: <20220304195238.1141725-1-decot+git@google.com>
Date:   Fri,  4 Mar 2022 11:52:38 -0800
From:   David Decotigny <decot+git@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>, linux-kernel@...r.kernel.org
Cc:     David Decotigny <ddecotig@...gle.com>
Subject: [PATCH v1 1/1] irqchip/gic-v3-its: fixup IRQ affinities to account
 for online CPUs

From: David Decotigny <ddecotig@...gle.com>

In some cases (eg. when booting with maxcpus=X), it is possible that
the preset IRQ affinity masks don't intersect with the set of online
CPUs. This patch extends the fallback strategy implemented when
IRQD_AFFINITY_MANAGED is not set to all cases. This is logged the
first time that happens.

Fixes: c5d6082d35e0 ("irqchip/gic-v3-its: Balance initial LPI affinity across CPUs")

---
 drivers/irqchip/irq-gic-v3-its.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index cd772973114a..de862fd9ad73 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -1618,11 +1618,6 @@ static int its_select_cpu(struct irq_data *d,
 		/* Try the intersection of the affinity and online masks */
 		cpumask_and(tmpmask, aff_mask, cpu_online_mask);
 
-		/* If that doesn't fly, the online mask is the last resort */
-		if (cpumask_empty(tmpmask))
-			cpumask_copy(tmpmask, cpu_online_mask);
-
-		cpu = cpumask_pick_least_loaded(d, tmpmask);
 	} else {
 		cpumask_and(tmpmask, irq_data_get_affinity_mask(d), cpu_online_mask);
 
@@ -1630,9 +1625,13 @@ static int its_select_cpu(struct irq_data *d,
 		if ((its_dev->its->flags & ITS_FLAGS_WORKAROUND_CAVIUM_23144) &&
 		    node != NUMA_NO_NODE)
 			cpumask_and(tmpmask, tmpmask, cpumask_of_node(node));
-
-		cpu = cpumask_pick_least_loaded(d, tmpmask);
 	}
+
+	/* If that doesn't fly, the online mask is the last resort */
+	if (WARN_ON_ONCE(cpumask_empty(tmpmask)))
+		cpumask_copy(tmpmask, cpu_online_mask);
+
+	cpu = cpumask_pick_least_loaded(d, tmpmask);
 out:
 	free_cpumask_var(tmpmask);
 
-- 
2.35.1.616.g0bdcbb4464-goog