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authorChristophe Leroy2017-12-18 11:08:29 +0100
committerLinus Walleij2017-12-20 10:28:05 +0100
commit7fda9100bb8258bbdff90f3db5079d28eb9b0013 (patch)
treef6927adaf0e19517d09d0dda7b12558dfdbe7b1e /include/linux/device.h
parentgpiolib: use kstrdup_const() for gpio_device label (diff)
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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 'include/linux/device.h')
-rw-r--r--include/linux/device.h3
1 files changed, 3 insertions, 0 deletions
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) \