From 7fda9100bb8258bbdff90f3db5079d28eb9b0013 Mon Sep 17 00:00:00 2001
From: Christophe Leroy <christophe.leroy@c-s.fr>
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 <christophe.leroy@c-s.fr>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
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 0bd472ffb0720..3b2465bbd5e70 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 9d32000725da8..46ac622e5c6ff 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) \
--
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