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

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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>
This commit is contained in:
Christophe Leroy 2017-12-18 11:08:35 +01:00 • committed by Linus Walleij
commit 1efba35afa
1 changed files with 7 additions and 2 deletions
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9
drivers/gpio/gpiolib-sysfs.c
View file

@ -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);
@ -133,7 +134,11 @@ static ssize_t value_store(struct device *dev,
} else {
long value;
status = kstrtol(buf, 0, &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);
status = size;