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From: Bartosz Golaszewski <brgl@bgdev.pl>
To: Kent Gibson <warthog618@gmail.com>
Cc: Linus Walleij <linus.walleij@linaro.org>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	Andy Shevchenko <andy.shevchenko@gmail.com>,
	Maxim Kochetkov <fido_max@inbox.ru>
Subject: Re: gpiolib gpio_chrdev_release duration is about 30 ms
Date: Sun, 26 Jul 2020 13:04:56 +0200
Message-ID: <CAMRc=MezeYSLCMpDdfZeUteg5ZXBO_1V+8R-mnDZYXZLZ3HDDQ@mail.gmail.com> (raw)
In-Reply-To: <20200725035203.GA8572@sol>

On Sat, Jul 25, 2020 at 5:52 AM Kent Gibson <warthog618@gmail.com> wrote:
>
> On Fri, Jul 24, 2020 at 09:36:03PM +0200, Bartosz Golaszewski wrote:
> > 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.
> >
>
> That patch is post the cdev split, so it certainly wont apply to an
> older kernel.  I'm happy to backport it if you need it - just
> nominate the branch you want it for.
>
> Cheers,
> Kent.

Linus' devel branch is fine - I haven't picked up new patches in past weeks.

Bartosz

  reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 12:56 Maxim Kochetkov
2020-07-17 13:37 ` Linus Walleij
2020-07-17 13:44   ` Maxim Kochetkov
2020-07-17 14:17   ` Maxim Kochetkov
2020-07-17 15:07     ` Andy Shevchenko
2020-07-18  4:25       ` Kent Gibson
2020-07-20  8:14         ` Maxim Kochetkov
2020-07-24 19:36           ` Bartosz Golaszewski
2020-07-25  3:52             ` Kent Gibson
2020-07-26 11:04               ` Bartosz Golaszewski [this message]
2020-07-26 22:32               ` Linus Walleij

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