On Thu, Jul 24 2025 at 07:18, Jiri Slaby wrote:
> 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"?
A 64-bit division is definitely more expensive than a shift operation
and on 32-bit w/o a 64-bit divide instruction it's more than horribly
slow.
> Or instead, you could store the diff in irqhandler_duration_threshold_ns
> (mind that "_ns") and avoid the shift and div completely.
That's the right thing to do. The setup code can do a *1000 and be done.
> And what about the wrap? Don't you need abs_diff()?
~500 years after boot :)
Thanks,
tglx
