lkml.org 
[lkml]   [2017]   [Dec]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 4/4] gpio: sysfs: avoid using kstrtol() in 'value' attribute write
Date
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>
---
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 bb10e8ed456e..31e2352632a2 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;
--
2.13.3
\
 
 \ /
  Last update: 2017-12-18 11:09    [W:0.063 / U:0.676 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site