From 51b55a8399c420b6dfd9f23a95b4787b1909e9c9 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@kernel.org>
Date: Fri, 3 Jul 2009 08:29:57 -0500
Subject: [PATCH 019/183] genirq: Disable irqfixup/poll on PREEMPT_RT.

The support for misrouted IRQs is used on old / legacy systems and is
not feasible on PREEMPT_RT.

Polling for interrupts reduces the overall system performance.
Additionally the interrupt latency depends on the polling frequency and
delays are not desired for real time workloads.

Disable IRQ polling on PREEMPT_RT and let the user know that it is not
enabled. The compiler will optimize the real fixup/poll code out.

[ bigeasy: Update changelog and switch to IS_ENABLED() ]

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210917223841.c6j6jcaffojrnot3@linutronix.de
---
 kernel/irq/spurious.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/irq/spurious.c b/kernel/irq/spurious.c
index c481d8458325..02b2daf07441 100644
--- a/kernel/irq/spurious.c
+++ b/kernel/irq/spurious.c
@@ -447,6 +447,10 @@ MODULE_PARM_DESC(noirqdebug, "Disable irq lockup detection when true");
 
 static int __init irqfixup_setup(char *str)
 {
+	if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+		pr_warn("irqfixup boot option not supported with PREEMPT_RT\n");
+		return 1;
+	}
 	irqfixup = 1;
 	printk(KERN_WARNING "Misrouted IRQ fixup support enabled.\n");
 	printk(KERN_WARNING "This may impact system performance.\n");
@@ -459,6 +463,10 @@ module_param(irqfixup, int, 0644);
 
 static int __init irqpoll_setup(char *str)
 {
+	if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+		pr_warn("irqpoll boot option not supported with PREEMPT_RT\n");
+		return 1;
+	}
 	irqfixup = 2;
 	printk(KERN_WARNING "Misrouted IRQ fixup and polling support "
 				"enabled\n");
-- 
2.47.1

