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[PATCH v4] genirq: add support for warning on long-running IRQ handlers

Wladislav Wiebe posted 1 patch 2 months, 1 week ago
There is a newer version of this series
.../admin-guide/kernel-parameters.txt         |  5 ++
kernel/irq/handle.c                           | 49 ++++++++++++++++++-
2 files changed, 53 insertions(+), 1 deletion(-)
[PATCH v4] genirq: add support for warning on long-running IRQ handlers
Posted by Wladislav Wiebe 2 months, 1 week ago 
Introduce a mechanism to detect and warn about prolonged IRQ handlers.
With a new command-line parameter (irqhandler.duration_warn_us=),
users can configure the duration threshold in microseconds when a warning
in such format should be emitted:

"[CPU14] long duration of IRQ[159:bad_irq_handler [long_irq]], took: 1330 us"

The implementation uses local_clock() to measure the execution duration of the
generic IRQ per-CPU event handler.

Signed-off-by: Wladislav Wiebe <wladislav.wiebe@nokia.com>
---
V3 -> V4: convert us to ns in setup path to avoid shift operation in compare path
	  based on V3 review:
	  https://lore.kernel.org/lkml/20250723182836.1177-1-wladislav.wiebe@nokia.com/
V2 -> V3: Addressed review comments based on v2:
	  https://lore.kernel.org/lkml/20250714084209.918-1-wladislav.wiebe@nokia.com/
	  - refactor commit message
	  - switch from early_param() to __setup()
	  - comment on approximation of nano to microseconds conversion
	  - move ts_start to if() branch
	  - align pr_warn arguments
	  - surround else block with brackets as well
	  - invert the condition and drop the "else {}" in cmdline arg. check
	  - make struct irqaction *action function param. const
	    in irqhandler_duration_check()
	  - print smp_processor_id() return as unsigned int
	  - fix warning text "on IRQ[...]" -> "of IRQ[...]"
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                           | 49 ++++++++++++++++++-
 2 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index e4b7015718bb..441943dfd0f3 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2259,6 +2259,11 @@
 			for it. Intended to get systems with badly broken
 			firmware running.
 
+	irqhandler.duration_warn_us= [KNL]
+			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 088e5c01075c..4233ead7cbc3 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -141,6 +141,44 @@ 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_ns __ro_after_init;
+
+static int __init irqhandler_duration_check_setup(char *arg)
+{
+	unsigned long val;
+	int ret;
+
+	ret = kstrtoul(arg, 0, &val);
+	if (ret) {
+		pr_err("Unable to parse irqhandler.duration_warn_us setting: ret=%d\n", ret);
+		return 0;
+	}
+
+	if (!val) {
+		pr_err("Invalid irqhandler.duration_warn_us setting, must be > 0\n");
+		return 0;
+	}
+
+	irqhandler_duration_threshold_ns = val * 1000;
+	static_branch_enable(&irqhandler_duration_check_enabled);
+
+	return 1;
+}
+__setup("irqhandler.duration_warn_us=", irqhandler_duration_check_setup);
+
+static inline void irqhandler_duration_check(u64 ts_start, unsigned int irq,
+					     const struct irqaction *action)
+{
+	u64 delta_ns = local_clock() - ts_start;
+
+	if (unlikely(delta_ns > irqhandler_duration_threshold_ns)) {
+		pr_warn_ratelimited("[CPU%u] long duration of IRQ[%u:%ps], took: %llu us\n",
+				    smp_processor_id(), irq, action->handler,
+				    delta_ns >> 10);
+	}
+}
+
 irqreturn_t __handle_irq_event_percpu(struct irq_desc *desc)
 {
 	irqreturn_t retval = IRQ_NONE;
@@ -160,7 +198,16 @@ irqreturn_t __handle_irq_event_percpu(struct irq_desc *desc)
 			lockdep_hardirq_threaded();
 
 		trace_irq_handler_entry(irq, action);
-		res = action->handler(irq, action->dev_id);
+
+		if (static_branch_unlikely(&irqhandler_duration_check_enabled)) {
+			u64 ts_start = local_clock();
+
+			res = action->handler(irq, action->dev_id);
+			irqhandler_duration_check(ts_start, irq, action);
+		} else {
+			res = action->handler(irq, action->dev_id);
+		}
+
 		trace_irq_handler_exit(irq, action, res);
 
 		if (WARN_ONCE(!irqs_disabled(),"irq %u handler %pS enabled interrupts\n",
-- 
2.39.3.dirty
Re: [PATCH v4] genirq: add support for warning on long-running IRQ handlers
Posted by Jiri Slaby 2 months ago 
On 24. 07. 25, 17:50, Wladislav Wiebe wrote:
> Introduce a mechanism to detect and warn about prolonged IRQ handlers.
> With a new command-line parameter (irqhandler.duration_warn_us=),
> users can configure the duration threshold in microseconds when a warning
> in such format should be emitted:
> 
> "[CPU14] long duration of IRQ[159:bad_irq_handler [long_irq]], took: 1330 us"
> 
> The implementation uses local_clock() to measure the execution duration of the
> generic IRQ per-CPU event handler.


This version LGTM

Reviewed-by: Jiri Slaby <jirislaby@kernel.org>

> --- a/kernel/irq/handle.c
> +++ b/kernel/irq/handle.c
...
> +static inline void irqhandler_duration_check(u64 ts_start, unsigned int irq,
> +					     const struct irqaction *action)
> +{
> +	u64 delta_ns = local_clock() - ts_start;
> +
> +	if (unlikely(delta_ns > irqhandler_duration_threshold_ns)) {
> +		pr_warn_ratelimited("[CPU%u] long duration of IRQ[%u:%ps], took: %llu us\n",
> +				    smp_processor_id(), irq, action->handler,
> +				    delta_ns >> 10);

Only that: would the division matter in here? Or print ns? But feel free 
to ignore this.

thanks,
-- 
js
suse labs
Re: [PATCH v4] genirq: add support for warning on long-running IRQ handlers
Posted by Wladislav Wiebe 2 months ago 
On 31/07/2025 09:46, Jiri Slaby wrote:
>
>
> On 24. 07. 25, 17:50, Wladislav Wiebe wrote:
>> Introduce a mechanism to detect and warn about prolonged IRQ handlers.
>> With a new command-line parameter (irqhandler.duration_warn_us=),
>> users can configure the duration threshold in microseconds when a warning
>> in such format should be emitted:
>>
>> "[CPU14] long duration of IRQ[159:bad_irq_handler [long_irq]], took: 1330 us"
>>
>> The implementation uses local_clock() to measure the execution duration of the
>> generic IRQ per-CPU event handler.
>
>
> This version LGTM
>
> Reviewed-by: Jiri Slaby <jirislaby@kernel.org>

Thanks a lot!

>
>> --- a/kernel/irq/handle.c
>> +++ b/kernel/irq/handle.c
> ...
>> +static inline void irqhandler_duration_check(u64 ts_start, unsigned int irq,
>> +                                          const struct irqaction *action)
>> +{
>> +     u64 delta_ns = local_clock() - ts_start;
>> +
>> +     if (unlikely(delta_ns > irqhandler_duration_threshold_ns)) {
>> +             pr_warn_ratelimited("[CPU%u] long duration of IRQ[%u:%ps], took: %llu us\n",
>> +                                 smp_processor_id(), irq, action->handler,
>> +                                 delta_ns >> 10);
>
> Only that: would the division matter in here? Or print ns? But feel free
> to ignore this.

In principle one could think when the paramater interface is provided in microseconds,
the duration print might be in the same resolution - hmm.

However, for the division part I have no objection going with
precise devision as we are kind of no longer in the "fast-path", hence v5 prepared:
https://lore.kernel.org/lkml/20250804093525.851-1-wladislav.wiebe@nokia.com/

Thank you
- W.W.

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