linux-kernel - Re: [PATCH v2] genirq: add support for warning on long-running IRQ handlers

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Message-ID: <adbc919f-772b-46f1-99fb-d05cf0989763@kernel.org>
Date: Tue, 22 Jul 2025 10:21:47 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Wladislav Wiebe <wladislav.wiebe@...ia.com>, tglx@...utronix.de,
 corbet@....net
Cc: akpm@...ux-foundation.org, paulmck@...nel.org, rostedt@...dmis.org,
 Neeraj.Upadhyay@....com, david@...hat.com, bp@...en8.de, arnd@...db.de,
 fvdl@...gle.com, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 peterz@...radead.org
Subject: Re: [PATCH v2] genirq: add support for warning on long-running IRQ
 handlers

On 14. 07. 25, 10:41, Wladislav Wiebe wrote:
> This patch adds a mechanism to detect and warn about long-running IRQ
> handlers exceeding a user-defined duration threshold in microseconds.
> 
> The feature is enabled via the kernel boot parameter:
> "irqhandler.duration_warn_us=<threshold_in_us>"
> 
> For example, passing irqhandler.duration_warn_us=1000 will warn if an
> IRQ handler takes more than 1000 microseconds.
> 
> Implementation uses local_clock() to measure the execution duration of
> IRQ handlers. When the threshold is exceeded, a ratelimited warning is
> printed:
> 
> "[CPU14] long duration on IRQ[159:bad_irq_handler [long_irq]], took: 1330 us"
> 
> Signed-off-by: Wladislav Wiebe <wladislav.wiebe@...ia.com>
> ---
> V1 -> V2: refactor to use local_clock() instead of jiffies and replace
> 	  Kconfig knobs by a new command-line parameter.
> V1 link:  https://lore.kernel.org/lkml/20250630124721.18232-1-wladislav.wiebe@nokia.com/
> ---
>   .../admin-guide/kernel-parameters.txt         |  5 ++
>   kernel/irq/handle.c                           | 48 ++++++++++++++++++-
>   2 files changed, 52 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index f1f2c0874da9..fa89f21ea1e6 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2543,6 +2543,11 @@
>   			for it. Intended to get systems with badly broken
>   			firmware running.
>   
> +	irqhandler.duration_warn_us= [KNL,EARLY]
> +			Warn if an IRQ handler exceeds the specified duration
> +			threshold in microseconds. Useful for identifying
> +			long-running IRQs in the system.
> +
>   	irqpoll		[HW]
>   			When an interrupt is not handled search all handlers
>   			for it. Also check all handlers each timer
> diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
> index 9489f93b3db3..eab8fdfab8d8 100644
> --- a/kernel/irq/handle.c
> +++ b/kernel/irq/handle.c
> @@ -136,6 +136,44 @@ void __irq_wake_thread(struct irq_desc *desc, struct irqaction *action)
>   	wake_up_process(action->thread);
>   }
>   
> +static DEFINE_STATIC_KEY_FALSE(irqhandler_duration_check_enabled);
> +static u64 irqhandler_duration_threshold_us __ro_after_init;
> +
> +static int __init irqhandler_duration_check_setup(char *arg)
> +{
> +	unsigned long val;
> +	int ret;
> +
> +	if (!arg)
> +		return 0;
> +
> +	ret = kstrtoul(arg, 0, &val);
> +	if (ret)
> +		return ret;
> +
> +	if (val > 0) {
> +		irqhandler_duration_threshold_us = val;
> +		static_branch_enable(&irqhandler_duration_check_enabled);
> +	} else {
> +		pr_err("Invalid irqhandler.duration_warn_us setting (%lu)\n", val);
> +		return -EINVAL;

Perhaps invert the condition and drop the "else {}"?

> +	}
> +
> +	return 0;
> +}
> +early_param("irqhandler.duration_warn_us", irqhandler_duration_check_setup);
> +
> +static inline void irqhandler_duration_check(u64 ts_start, unsigned int irq,
> +					      struct irqaction *action)

Can be const.

> +{
> +	u64 delta_us = (local_clock() - ts_start) >> 10;
> +
> +	if (unlikely(delta_us > irqhandler_duration_threshold_us)) {
> +		pr_warn_ratelimited("[CPU%d] long duration on IRQ[%u:%ps], took: %llu us\n",

s/%d/%u/.
Do you mean "of IRQ[...]"?

> +			smp_processor_id(), irq, action->handler, delta_us);
> +	}
> +}
> +
>   irqreturn_t __handle_irq_event_percpu(struct irq_desc *desc)
>   {
>   	irqreturn_t retval = IRQ_NONE;

thanks,
-- 
js
suse labs