Commit 1efba35a authored Dec 18, 2017 by Christophe Leroy Committed by Linus Walleij Dec 20, 2017

gpio: sysfs: avoid using kstrtol() in 'value' attribute write



A 'perf record' on an app continuously writing in the 'value'
attribute show that most of the time is spent in kstrtol()

--17.99%--value_store
          |
          |--10.17%--kstrtoint
          |          |
          |          |--8.82%--kstrtoll
          |
          |--2.50%--gpiod_set_value_cansleep
          |
          |--1.82%--u16_gpio_set
          |
          |--1.46%--value_store

The normal case is to write 0 or 1 in the attribute, therefore
this patch avoids the call to kstrtol() in the most common cases

Then 'perf record' shows

--7.21%--value_store
          |
          |--2.69%--u16_gpio_set
          |
          |--1.47%--value_store
          |
          |--1.08%--gpiod_set_value_cansleep
          |
          |--0.60%--mutex_lock
          |
           --0.58%--mutex_unlock

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

parent 7a94b88c

drivers/gpio/gpiolib-sysfs.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -8,6 +8,7 @@
		#include <linux/interrupt.h>
		#include <linux/kdev_t.h>
		#include <linux/slab.h>
		#include <linux/ctype.h>

		#include "gpiolib.h"

		@@ -124,7 +125,7 @@ static ssize_t value_store(struct device *dev,
		{
		struct gpiod_data *data = dev_get_drvdata(dev);
		struct gpio_desc *desc = data->desc;
		ssize_t status;
		ssize_t status = 0;

		mutex_lock(&data->mutex);

		@@ -133,6 +134,10 @@ static ssize_t value_store(struct device *dev,
		} else {
		long value;

		if (size <= 2 && isdigit(buf[0]) &&
		(size == 1 \|\| buf[1] == '\n'))
		value = buf[0] - '0';
		else
		status = kstrtol(buf, 0, &value);
		if (status == 0) {
		gpiod_set_value_cansleep(desc, value);