Re: gpiolib gpio_chrdev_release duration is about 30 ms

[Bartosz Golaszewski <brgl@bgdev.pl>]

On Mon, Jul 20, 2020 at 10:14 AM Maxim Kochetkov <fido_max@inbox.ru> wrote:
>
> It works fine with this patch. Thank you so much!
>
> 18.07.2020 07:25, Kent Gibson пишет:
> > On Fri, Jul 17, 2020 at 06:07:04PM +0300, Andy Shevchenko wrote:
> >> On Fri, Jul 17, 2020 at 5:17 PM Maxim Kochetkov <fido_max@inbox.ru> wrote:
> >>>
> >>> I need a small userspace program to do some GPIO magic to communicate
> >>> other hardware like devmem. This program takes about 2,5 seconds just to
> >>> find GPIO lines by name.
> >>>
> >>> replacing synchronize_rcu to synchronize_rcu_expedited in
> >>> atomic_notifier_chain_unregister gives the same boost as removing
> >>> synchronize_rcu
> >>
> >> Have you tried to replace an atomic notifier call with a regular one?
> >> IIRC it's still not clear why atomic is used there.
> >>
> >
> > Indeed, I recently submitted a patch to switch the
> > atomic_notifier_call_chain to blocking_notifier_call_chain, as some of
> > the chained calls can sleep.
> > Not sure if that is related, or if the change would make this case better
> > or worse, but it would be interesting to find out.
> > The patch is in the current gpio/devel, btw.
> >
> > Cheers,
> > Kent.
> >

Linus,

I think we should consider submitting this patch for stable then
because this slow-down was affects previously existing use-cases.

Bartosz