diff options
| author | Christophe Leroy <christophe.leroy@c-s.fr> | 2017-12-18 13:08:29 +0300 |
|---|---|---|
| committer | Linus Walleij <linus.walleij@linaro.org> | 2017-12-20 12:28:05 +0300 |
| commit | 7fda9100bb8258bbdff90f3db5079d28eb9b0013 (patch) | |
| tree | f6927adaf0e19517d09d0dda7b12558dfdbe7b1e /drivers/gpio/gpiolib-sysfs.c | |
| parent | fcf273e5807976009dbb5ffb00bd5b9091843fe6 (diff) | |
| download | linux-7fda9100bb8258bbdff90f3db5079d28eb9b0013.tar.xz | |
gpio: sysfs: change 'value' attribute to prealloc
The GPIO 'value' attribute is time critical. A small bench with
'perf record' on the app below shows that 80% of the time spent in
sysfs_kf_seq_show() is spent in memset() for zeroising the buffer.
|--67.48%--sysfs_kf_seq_show
| |
| |--54.40%--memset
| |
| |--11.49%--dev_attr_show
| | |
| | |--10.06%--value_show
| | | |
| | | |--4.75%--sprintf
| | | | |
This patch changes the attribute type to prealloc, eliminating the
need to zeroise the buffer at each read. 'perf record' gives the
following result.
|--42.41%--sysfs_kf_read
| |
| |--39.73%--dev_attr_show
| | |
| | |--38.23%--value_show
| | | |
| | | |--29.22%--sprintf
| | | | |
Test done with the following small app:
int main(int argc, char **argv)
{
int fd = open(argv[1], O_RDONLY);
for (;;) {
int buf[512];
read(fd, buf, 512);
lseek(fd, 0, SEEK_SET);
}
exit(0);
}
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Diffstat (limited to 'drivers/gpio/gpiolib-sysfs.c')
| -rw-r--r-- | drivers/gpio/gpiolib-sysfs.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c index 0bd472ffb072..3b2465bbd5e7 100644 --- a/drivers/gpio/gpiolib-sysfs.c +++ b/drivers/gpio/gpiolib-sysfs.c @@ -138,7 +138,7 @@ static ssize_t value_store(struct device *dev, return status; } -static DEVICE_ATTR_RW(value); +static DEVICE_ATTR_PREALLOC(value, S_IWUSR | S_IRUGO, value_show, value_store); static irqreturn_t gpio_sysfs_irq(int irq, void *priv) { |