From 7fda9100bb8258bbdff90f3db5079d28eb9b0013 Mon Sep 17 00:00:00 2001 From: Christophe Leroy Date: Mon, 18 Dec 2017 11:08:29 +0100 Subject: [PATCH] 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 Signed-off-by: Linus Walleij --- drivers/gpio/gpiolib-sysfs.c | 2 +- include/linux/device.h | 3 +++ 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c index 0bd472f..3b2465b 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 9d32000..46ac622 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) \ -- 2.7.4