linux-kernel - [PATCH] genirq: Limit irq_calc_affinity

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Date:   Fri, 22 Jan 2021 08:47:46 +0000
From:   Liu Chao <liuchao173@...wei.com>
To:     <tglx@...utronix.de>, <linux-kernel@...r.kernel.org>
CC:     <hushiyuan@...wei.com>, <hewenliang4@...wei.com>
Subject: [PATCH] genirq: Limit irq_calc_affinity_vectors to housekeeping CPUs

Replace the cpumask used in irq_calc_affinity_vectors from all possible
CPUs to only housekeeping CPUs.

When we have isolated CPUs used by real-time tasks, IRQs will be move to
housekeeping CPUs.

If there are too many IRQ vectors, moving the all to housekeeping CPUs may
exceed per-CPU vector limits. For example, when I only have two
housekeeping CPUs, there are dozens of IRQs on two CPUs, but actually one
IRQ per housekeeping CPU is enough.

Signed-off-by: Liu Chao <liuchao173@...wei.com>
---
 kernel/irq/affinity.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
index 4d89ad4fae3b..3f22e3314e1b 100644
--- a/kernel/irq/affinity.c
+++ b/kernel/irq/affinity.c
@@ -8,6 +8,7 @@
 #include <linux/slab.h>
 #include <linux/cpu.h>
 #include <linux/sort.h>
+#include <linux/sched/isolation.h>
 
 static void irq_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
 				unsigned int cpus_per_vec)
@@ -506,7 +507,8 @@ unsigned int irq_calc_affinity_vectors(unsigned int minvec, unsigned int maxvec,
 		set_vecs = maxvec - resv;
 	} else {
 		get_online_cpus();
-		set_vecs = cpumask_weight(cpu_possible_mask);
+		set_vecs = cpumask_weight(
+				housekeeping_cpumask(HK_FLAG_MANAGED_IRQ));
 		put_online_cpus();
 	}
 
-- 
2.23.0