Hi!
> > --- a/drivers/leds/led-triggers.c
> > +++ b/drivers/leds/led-triggers.c
> > @@ -378,14 +378,15 @@ void led_trigger_event(struct led_trigger *trig,
> > enum led_brightness brightness)
> > {
> > struct led_classdev *led_cdev;
> > + unsigned long flags;
> >
> > if (!trig)
> > return;
> >
> > - read_lock(&trig->leddev_list_lock);
> > + read_lock_irqsave(&trig->leddev_list_lock, flags);
> > list_for_each_entry(led_cdev, &trig->led_cdevs, trig_list)
> > led_set_brightness(led_cdev, brightness);
> > - read_unlock(&trig->leddev_list_lock);
> > + read_unlock_irqrestore(&trig->leddev_list_lock, flags);
> > }
> > EXPORT_SYMBOL_GPL(led_trigger_event);
>
> meanwhile this patch hit v5.10.x stable and caused a performance
> degradation on our use case:
>
> It's an embedded ARM system, 4x Cortex A53, with an SPI attached CAN
> controller. CAN stands for Controller Area Network and here used to
> connect to some automotive equipment. Over CAN an ISOTP (a CAN-specific
> Transport Protocol) transfer is running. With this patch, we see CAN
> frames delayed for ~6ms, the usual gap between CAN frames is 240µs.
>
> Reverting this patch, restores the old performance.
>
> What is the best way to solve this dilemma? Identify the critical path
> in our use case? Is there a way we can get around the irqsave in
> led_trigger_event()?
Hans was pushing for this patch, perhaps he has some ideas...
Pavel
--
http://www.livejournal.com/~pavelmachek
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