From 1efba35afae43094d3f26093f5f1ab8a46686a6f Mon Sep 17 00:00:00 2001
From: Christophe Leroy <christophe.leroy@c-s.fr>
Date: Mon, 18 Dec 2017 11:08:35 +0100
Subject: [PATCH] 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>
---
drivers/gpio/gpiolib-sysfs.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index ad7173df72eb5..3dbaf489a8a52 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;
--
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