Re: gpiolib gpio_chrdev_release duration is about 30 ms

[Kent Gibson <warthog618@xxxxxxxxx>]

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@xxxxxxxx> 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.