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

[Jiri Slaby]

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