linux-kernel - [PATCH] genirq: Disable irqpoll on PREEMPT

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Message-ID: <20210917223841.c6j6jcaffojrnot3@linutronix.de>
Date:   Sat, 18 Sep 2021 00:38:41 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-kernel@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH] genirq: Disable irqpoll on PREEMPT_RT.

From: Ingo Molnar <mingo@...nel.org>
Date: Fri, 3 Jul 2009 08:29:57 -0500

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 workload.

Disable IRQ polling on PREEMPT_RT and let the user know that it is not
enabled.

[ bigeasy: changelog, IS_ENABLED ]

Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 kernel/irq/spurious.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/irq/spurious.c b/kernel/irq/spurious.c
index c481d84583257..02b2daf074414 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");
-- 
2.33.0