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>
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 @@
#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) \