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authorChristophe Leroy <christophe.leroy@c-s.fr>2017-12-18 11:08:35 +0100
committerLinus Walleij <linus.walleij@linaro.org>2017-12-20 10:34:58 +0100
commit1efba35afae43094d3f26093f5f1ab8a46686a6f (patch)
tree5f0cc54ea8cd6826f8daa5d17410b7c9e6f19f8f
parent7a94b88cb7087aa3184161bedccfea25e5502c62 (diff)
downloadlinux-1efba35afae43094d3f26093f5f1ab8a46686a6f.tar.bz2
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>
-rw-r--r--drivers/gpio/gpiolib-sysfs.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index ad7173df72eb..3dbaf489a8a5 100644
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -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;