[RFC PATCH v3 2/3] genirq/cpuhotplug: Adjust managed irqs according to change of housekeeping CPU

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Interrupts disturb real-time tasks on affined cpus.
To ensure CPU isolation for real-time tasks, interrupt handling must
be adjusted accordingly.
Non-managed interrupts can be configured from userspace,
while managed interrupts require adjustments in kernelspace.

Adjust status of managed interrupts according change
of housekeeping CPUs to support dynamic CPU isolation.

Signed-off-by: Costa Shulyupin <costa.shul@xxxxxxxxxx>

---

The following code is a proof of concept to validate
and review the correctness of the approach to solving the problem.

C++ comments denote temporary comments.

v2:
- refactor irq_affinity_adjust():
- add more comments
- add managed_irq_isolate() derived from migrate_one_irq(),
  irq_needs_fixup() and irq_fixup_move_pending()
- use irq_set_affinity() instead of irq_set_affinity_locked
- Addressed Gleixner's comments:
- use `struct cpumask *` instead of `cpumask_var_t` in function signature
- remove locking in irq_affinity_adjust()

v1:
- https://lore.kernel.org/lkml/20240516190437.3545310-5-costa.shul@xxxxxxxxxx/
---
 include/linux/irq.h      |  2 +
 kernel/cgroup/cpuset.c   |  1 +
 kernel/irq/cpuhotplug.c  | 95 ++++++++++++++++++++++++++++++++++++++++
 kernel/sched/isolation.c | 10 ++++-
 4 files changed, 107 insertions(+), 1 deletion(-)

diff --git a/include/linux/irq.h b/include/linux/irq.h
index fa711f80957b6..4eb2e765dbd95 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -619,6 +619,8 @@ extern int irq_affinity_online_cpu(unsigned int cpu);
 # define irq_affinity_online_cpu	NULL
 #endif
 
+int managed_irq_affinity_adjust(struct cpumask *enable_mask);
+
 #if defined(CONFIG_SMP) && defined(CONFIG_GENERIC_PENDING_IRQ)
 void __irq_move_irq(struct irq_data *data);
 static inline void irq_move_irq(struct irq_data *data)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index bf60bdc973dd6..73b06b2cd91e3 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -90,6 +90,7 @@ static struct list_head remote_children;
 #define HOUSEKEEPING_FLAGS	(BIT(HK_TYPE_TIMER)  | BIT(HK_TYPE_RCU)  |\
 				 BIT(HK_TYPE_SCHED)  | BIT(HK_TYPE_MISC) |\
 				 BIT(HK_TYPE_DOMAIN) | BIT(HK_TYPE_WQ)   |\
+				 BIT(HK_TYPE_MANAGED_IRQ) |\
 				 BIT(HK_TYPE_KTHREAD))
 
 /*
diff --git a/kernel/irq/cpuhotplug.c b/kernel/irq/cpuhotplug.c
index ec2cdcd20bee7..adbe1f3e5bd22 100644
--- a/kernel/irq/cpuhotplug.c
+++ b/kernel/irq/cpuhotplug.c
@@ -252,3 +252,98 @@ int irq_affinity_online_cpu(unsigned int cpu)
 
 	return 0;
 }
+
+/*
+ * managed_irq_isolate() - Deactivate managed interrupts if necessary
+ */
+// derived from migrate_one_irq, irq_needs_fixup, irq_fixup_move_pending
+static int managed_irq_isolate(struct irq_desc *desc)
+{
+	struct irq_data *d = irq_desc_get_irq_data(desc);
+	struct irq_chip *chip = irq_data_get_irq_chip(d);
+	const struct cpumask *a;
+	bool maskchip;
+	int err;
+
+	/*
+	 * Deactivate if:
+	 * - Interrupt is managed
+	 * - Interrupt is not per cpu
+	 * - Interrupt is started
+	 * - Effective affinity mask includes isolated CPUs
+	 */
+	if (!irqd_affinity_is_managed(d) || irqd_is_per_cpu(d) || !irqd_is_started(d)
+	    || cpumask_subset(irq_data_get_effective_affinity_mask(d),
+			      housekeeping_cpumask(HK_TYPE_MANAGED_IRQ)))
+		return 0;
+	// TBD: it is required?
+	/*
+	 * Complete an eventually pending irq move cleanup. If this
+	 * interrupt was moved in hard irq context, then the vectors need
+	 * to be cleaned up. It can't wait until this interrupt actually
+	 * happens and this CPU was involved.
+	 */
+	irq_force_complete_move(desc);
+
+	if (irqd_is_setaffinity_pending(d)) {
+		irqd_clr_move_pending(d);
+		if (cpumask_intersects(desc->pending_mask,
+		    housekeeping_cpumask(HK_TYPE_MANAGED_IRQ)))
+			a = irq_desc_get_pending_mask(desc);
+	} else {
+		a = irq_data_get_affinity_mask(d);
+	}
+
+	maskchip = chip->irq_mask && !irq_can_move_pcntxt(d) && !irqd_irq_masked(d);
+	if (maskchip)
+		chip->irq_mask(d);
+
+	if (!cpumask_intersects(a, housekeeping_cpumask(HK_TYPE_MANAGED_IRQ))) {
+		/*
+		 * Shut managed interrupt down and leave the affinity untouched.
+		 * The effective affinity is reset to the first online CPU.
+		 */
+		irqd_set_managed_shutdown(d);
+		irq_shutdown_and_deactivate(desc);
+		return 0;
+	}
+
+	/*
+	 * Do not set the force argument of irq_do_set_affinity() as this
+	 * disables the masking of offline CPUs from the supplied affinity
+	 * mask and therefore might keep/reassign the irq to the outgoing
+	 * CPU.
+	 */
+	err = irq_do_set_affinity(d, a, false);
+	if (err)
+		pr_warn_ratelimited("IRQ%u: set affinity failed(%d).\n",
+				    d->irq, err);
+
+	if (maskchip)
+		chip->irq_unmask(d);
+
+	return err;
+}
+
+/** managed_irq_affinity_adjust() - Deactivate of restore managed interrupts
+ * according to change of housekeeping cpumask.
+ *
+ * @enable_mask:	CPUs for which interrupts should be restored
+ */
+int managed_irq_affinity_adjust(struct cpumask *enable_mask)
+{
+	unsigned int irq;
+
+	for_each_active_irq(irq) {
+		struct irq_desc *desc = irq_to_desc(irq);
+		unsigned int cpu;
+
+		for_each_cpu(cpu, enable_mask)
+			irq_restore_affinity_of_irq(desc, cpu);
+		raw_spin_lock(&desc->lock);
+		managed_irq_isolate(desc);
+		raw_spin_unlock(&desc->lock);
+	}
+
+	return 0;
+}
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 3f24921b929a0..cd72300ec8b99 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -130,6 +130,8 @@ static void __init housekeeping_setup_type(enum hk_type type,
  */
 static int housekeeping_update(enum hk_type type, const struct cpumask *update)
 {
+	int err = 0;
+
 	struct {
 		struct cpumask changed;
 		struct cpumask enable;
@@ -149,9 +151,15 @@ static int housekeeping_update(enum hk_type type, const struct cpumask *update)
 	if (!static_branch_unlikely(&housekeeping_overridden))
 		static_key_enable_cpuslocked(&housekeeping_overridden.key);
 
+	switch (type) {
+	case HK_TYPE_MANAGED_IRQ:
+		err = managed_irq_affinity_adjust(&masks->enable);
+		break;
+	default:
+	}
 	kfree(masks);
 
-	return 0;
+	return err;
 }
 
 static int __init housekeeping_setup(char *str, unsigned long flags)
-- 
2.45.0





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