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authorChristophe Leroy <christophe.leroy@c-s.fr>2017-12-18 11:08:29 +0100
committerLinus Walleij <linus.walleij@linaro.org>2017-12-20 10:28:05 +0100
commit7fda9100bb8258bbdff90f3db5079d28eb9b0013 (patch)
treef6927adaf0e19517d09d0dda7b12558dfdbe7b1e /drivers/gpio/gpiolib-sysfs.c
parentfcf273e5807976009dbb5ffb00bd5b9091843fe6 (diff)
downloadlwn-7fda9100bb8258bbdff90f3db5079d28eb9b0013.tar.gz
lwn-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>
Diffstat (limited to 'drivers/gpio/gpiolib-sysfs.c')
-rw-r--r--drivers/gpio/gpiolib-sysfs.c2
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)
{