linux-kernel - [RFC PATCH v4 2/4] genirq/cpuhotplug: Dynamically isolate CPUs from managed interrupts

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Message-ID: <20241201124244.997754-3-costa.shul@redhat.com>
Date: Sun,  1 Dec 2024 14:42:42 +0200
From: Costa Shulyupin <costa.shul@...hat.com>
To: longman@...hat.com,
	ming.lei@...hat.com,
	pauld@...hat.com,
	juri.lelli@...hat.com,
	vschneid@...hat.com,
	Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Koutný <mkoutny@...e.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Costa Shulyupin <costa.shul@...hat.com>,
	linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org
Subject: [RFC PATCH v4 2/4] genirq/cpuhotplug: Dynamically isolate CPUs from managed interrupts

After change of housekeeping_cpumask(HK_TYPE_MANAGED_IRQ) during runtime
managed interrupts continue to run on isolated CPUs.

Dynamic CPUs isolation is complex task. One of approaches is:
1. Set affected CPUs offline and disable relevant interrupts
2. Change housekeeping_cpumask
3. Set affected CPUs online and enable relevant interrupts

irq_restore_affinity_of_irq() restores managed interrupts
during complex CPU hotplug process of bringing back a CPU online.

Leave the interrupts disabled those affinity doesn't intersect
with new housekeeping_cpumask thereby ensuring isolation
of the CPU from managed intrrupts.

Signed-off-by: Costa Shulyupin <costa.shul@...hat.com>
---
 kernel/irq/cpuhotplug.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/irq/cpuhotplug.c b/kernel/irq/cpuhotplug.c
index ec2cdcd20bee..839d3e879c0d 100644
--- a/kernel/irq/cpuhotplug.c
+++ b/kernel/irq/cpuhotplug.c
@@ -218,6 +218,9 @@ static void irq_restore_affinity_of_irq(struct irq_desc *desc, unsigned int cpu)
 	if (desc->istate & IRQS_SUSPENDED)
 		return;

+	if (!cpumask_intersects(affinity, housekeeping_cpumask(HK_TYPE_MANAGED_IRQ)))
+		return;
+
 	if (irqd_is_managed_and_shutdown(data))
 		irq_startup(desc, IRQ_RESEND, IRQ_START_COND);

-- 
2.47.0