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gpio: sysfs: don't use sprintf() for 'value' attribute 

A bench with 'perf record' shows that most of time spent in value_show()
is spent in sprintf()

--42.41%--sysfs_kf_read
          |
          |--39.73%--dev_attr_show
          |          |
          |          |--38.23%--value_show
          |          |          |
          |          |          |--29.22%--sprintf
          |          |          |
          |          |          |--2.94%--gpiod_get_value_cansleep
          |          |          |

value_show() only returns "0\n" or "1\n", therefore the use of
sprintf() can be avoided

With this patch we get the following result with 'perf record'

--13.89%--sysfs_kf_read
          |
          |--10.72%--dev_attr_show
          |          |
          |          |--9.44%--value_show
          |          |          |
          |          |          |--4.61%--gpiod_get_value_cansleep

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 11:08:33 +01:00 committed by Linus Walleij
parent 9295c01253
commit 7a94b88cb7
1 changed files with 3 additions and 1 deletions
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4
drivers/gpio/gpiolib-sysfs.c
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@ -110,7 +110,9 @@ static ssize_t value_show(struct device *dev,
if (status < 0) if (status < 0)
goto err; goto err;
status = sprintf(buf, "%d\n", status); buf[0] = '0' + status;
buf[1] = '\n';
status = 2;
err: err:
mutex_unlock(&data->mutex); mutex_unlock(&data->mutex);