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From: Maxim Kochetkov <>
Subject: gpiolib gpio_chrdev_release duration is about 30 ms
Date: Fri, 17 Jul 2020 15:56:45 +0300
Message-ID: <> (raw)


I'm using libgpiod in userspace.
I have 6 gpiochip's on my board.
gpiod_line_find takes about 300ms to find GPIO line.

gpiod_line_find calls gpiod_foreach_chip
then gpiod_chip_iter_next
then gpiod_chip_close then close(chip->fd)
then we are going to kernel gpiolib gpio_chrdev_release
then atomic_notifier_chain_unregister
then synchronize_rcu()

synchronize_rcu takes about 30 ms (6*30ms=280ms)

I tried to remove synchronize_rcu from atomic_notifier_chain_unregister 
and gpiod_line_find takes about 2ms now.

             reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 12:56 Maxim Kochetkov [this message]
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
2020-07-26 22:32               ` Linus Walleij

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