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| author | Christophe Leroy <christophe.leroy@c-s.fr> | 2017-12-18 11:08:29 +0100 |
|---|---|---|
| committer | Linus Walleij <linus.walleij@linaro.org> | 2017-12-20 10:28:05 +0100 |
| commit | 7fda9100bb8258bbdff90f3db5079d28eb9b0013 (patch) | |
| tree | f6927adaf0e19517d09d0dda7b12558dfdbe7b1e | |
| parent | fcf273e5807976009dbb5ffb00bd5b9091843fe6 (diff) | |
| download | linux-stable-7fda9100bb8258bbdff90f3db5079d28eb9b0013.tar.gz linux-stable-7fda9100bb8258bbdff90f3db5079d28eb9b0013.tar.bz2 linux-stable-7fda9100bb8258bbdff90f3db5079d28eb9b0013.zip | |
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>
| -rw-r--r-- | drivers/gpio/gpiolib-sysfs.c | 2 | ||||
| -rw-r--r-- | include/linux/device.h | 3 |
2 files changed, 4 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) { diff --git a/include/linux/device.h b/include/linux/device.h index 9d32000725da..46ac622e5c6f 100644 --- a/include/linux/device.h +++ b/include/linux/device.h @@ -575,6 +575,9 @@ ssize_t device_store_bool(struct device *dev, struct device_attribute *attr, #define DEVICE_ATTR(_name, _mode, _show, _store) \ struct device_attribute dev_attr_##_name = __ATTR(_name, _mode, _show, _store) +#define DEVICE_ATTR_PREALLOC(_name, _mode, _show, _store) \ + struct device_attribute dev_attr_##_name = \ + __ATTR_PREALLOC(_name, _mode, _show, _store) #define DEVICE_ATTR_RW(_name) \ struct device_attribute dev_attr_##_name = __ATTR_RW(_name) #define DEVICE_ATTR_RO(_name) \ |