linux-kernel - Re: [PATCH v3] genirq: add support for warning on long-running IRQ handlers

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Message-ID: <aeeb783d-d921-450c-885d-c8e8b328f81b@kernel.org>
Date: Thu, 24 Jul 2025 07:18:10 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Wladislav Wiebe <wladislav.wiebe@...ia.com>, tglx@...utronix.de,
 corbet@....net, jirislaby@...nel.org
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 v3] genirq: add support for warning on long-running IRQ
 handlers

On 23. 07. 25, 20:28, 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.
...> +static inline void irqhandler_duration_check(u64 ts_start, 
unsigned int irq,
> +					     const struct irqaction *action)
> +{
> +	/* Approx. conversion to microseconds */
> +	u64 delta_us = (local_clock() - ts_start) >> 10;

Is this a microoptimization -- have you measured what speedup does it 
bring? IOW is it worth it instead of cleaner "/ NSEC_PER_USEC"?

Or instead, you could store the diff in irqhandler_duration_threshold_ns 
(mind that "_ns") and avoid the shift and div completely.

And what about the wrap? Don't you need abs_diff()?

thanks,
-- 
js
suse labs