[PATCH 1/4] gpio: sysfs: change 'value' attribute to prealloc

[PATCH 1/4] gpio: sysfs: change 'value' attribute to prealloc

[Christophe Leroy]

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>
---
 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 3f454eaf2101..7a3f4271393b 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 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) \
-- 
2.13.3

[PATCH 2/4] gpio: sysfs: correct error handling on 'value' attribute read.

[Christophe Leroy]

'value' attribute is supposed to only return 0 or 1 according to
the documentation.
With today's implementation, if gpiod_get_value_cansleep() fails
the printed 'value' is a negative value.

This patch ensures that an error is returned on read instead.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 drivers/gpio/gpiolib-sysfs.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index 7a3f4271393b..1b0f415df03b 100644
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -106,8 +106,12 @@ static ssize_t value_show(struct device *dev,
 
 	mutex_lock(&data->mutex);
 
-	status = sprintf(buf, "%d\n", gpiod_get_value_cansleep(desc));
+	status = gpiod_get_value_cansleep(desc);
+	if (status < 0)
+		goto err;
 
+	status = sprintf(buf, "%d\n", status);
+err:
 	mutex_unlock(&data->mutex);
 
 	return status;
-- 
2.13.3

[PATCH 3/4] gpio: sysfs: don't use sprintf() for 'value' attribute

[Christophe Leroy]

A bench with 'perf record' shows that most of time spent in value_show()
is spent in sprintf()

--42.41%--sysfs_kf_read
          |
          |--39.73%--dev_attr_show
          |          |
          |          |--38.23%--value_show
          |          |          |
          |          |          |--29.22%--sprintf
          |          |          |
          |          |          |--2.94%--gpiod_get_value_cansleep
          |          |          |

value_show() only returns "0\n" or "1\n", therefore the use of
sprintf() can be avoided

With this patch we get the following result with 'perf record'

--13.89%--sysfs_kf_read
          |
          |--10.72%--dev_attr_show
          |          |
          |          |--9.44%--value_show
          |          |          |
          |          |          |--4.61%--gpiod_get_value_cansleep

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 drivers/gpio/gpiolib-sysfs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index 1b0f415df03b..bb10e8ed456e 100644
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -110,7 +110,9 @@ static ssize_t value_show(struct device *dev,
 	if (status < 0)
 		goto err;
 
-	status = sprintf(buf, "%d\n", status);
+	buf[0] = '0' + status;
+	buf[1] = '\n';
+	status = 2;
 err:
 	mutex_unlock(&data->mutex);
 
-- 
2.13.3

[PATCH 4/4] gpio: sysfs: avoid using kstrtol() in 'value' attribute write

[Christophe Leroy]

A 'perf record' on an app continuously writing in the 'value'
attribute show that most of the time is spent in kstrtol()

--17.99%--value_store
          |
          |--10.17%--kstrtoint
          |          |
          |          |--8.82%--kstrtoll
          |
          |--2.50%--gpiod_set_value_cansleep
          |
          |--1.82%--u16_gpio_set
          |
          |--1.46%--value_store

The normal case is to write 0 or 1 in the attribute, therefore
this patch avoids the call to kstrtol() in the most common cases

Then 'perf record' shows

--7.21%--value_store
          |
          |--2.69%--u16_gpio_set
          |
          |--1.47%--value_store
          |
          |--1.08%--gpiod_set_value_cansleep
          |
          |--0.60%--mutex_lock
          |
           --0.58%--mutex_unlock

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 drivers/gpio/gpiolib-sysfs.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index bb10e8ed456e..31e2352632a2 100644
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -8,6 +8,7 @@
 #include <linux/interrupt.h>
 #include <linux/kdev_t.h>
 #include <linux/slab.h>
+#include <linux/ctype.h>
 
 #include "gpiolib.h"
 
@@ -124,7 +125,7 @@ static ssize_t value_store(struct device *dev,
 {
 	struct gpiod_data *data = dev_get_drvdata(dev);
 	struct gpio_desc *desc = data->desc;
-	ssize_t			status;
+	ssize_t status = 0;
 
 	mutex_lock(&data->mutex);
 
@@ -133,7 +134,11 @@ static ssize_t value_store(struct device *dev,
 	} else {
 		long		value;
 
-		status = kstrtol(buf, 0, &value);
+		if (size <= 2 && isdigit(buf[0]) &&
+		    (size == 1 || buf[1] == '\n'))
+			value = buf[0] - '0';
+		else
+			status = kstrtol(buf, 0, &value);
 		if (status == 0) {
 			gpiod_set_value_cansleep(desc, value);
 			status = size;
-- 
2.13.3

Re: [PATCH 1/4] gpio: sysfs: change 'value' attribute to prealloc

[Bartosz Golaszewski]

2017-12-18 11:08 GMT+01:00 Christophe Leroy <christophe.leroy@c-s.fr>:
> 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>
> ---
>  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 3f454eaf2101..7a3f4271393b 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 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) \
> --
> 2.13.3
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-gpio" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

I'm not sure we should be fixing performance issues in an interface
that's deprecated anyway...

The character device doesn't deal with strings so it will be much faster anyway.

Best regards,
Bartosz Golaszewski

Re: [PATCH 1/4] gpio: sysfs: change 'value' attribute to prealloc

[Christophe LEROY]

Le 18/12/2017 à 11:18, Bartosz Golaszewski a écrit :
> 2017-12-18 11:08 GMT+01:00 Christophe Leroy <christophe.leroy@c-s.fr>:
>> 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>
>> ---
>>   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 3f454eaf2101..7a3f4271393b 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 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) \
>> --
>> 2.13.3
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-gpio" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 
> I'm not sure we should be fixing performance issues in an interface
> that's deprecated anyway...

Many applications use that interface. I agree not to make deep changes 
for performance, but here the few changes are quite tiny, yet for a 
significant improvement, so aren't they worth it anyway ?

Christophe

> 
> The character device doesn't deal with strings so it will be much faster anyway.
> 
> Best regards,
> Bartosz Golaszewski
> 

Re: [PATCH 1/4] gpio: sysfs: change 'value' attribute to prealloc

[Bartosz Golaszewski]

2017-12-18 16:07 GMT+01:00 Christophe LEROY <christophe.leroy@c-s.fr>:
>
>
> Le 18/12/2017 à 11:18, Bartosz Golaszewski a écrit :
>>
>> 2017-12-18 11:08 GMT+01:00 Christophe Leroy <christophe.leroy@c-s.fr>:
>>>
>>> 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>
>>> ---
>>>   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 3f454eaf2101..7a3f4271393b 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 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) \
>>> --
>>> 2.13.3
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-gpio" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>>
>> I'm not sure we should be fixing performance issues in an interface
>> that's deprecated anyway...
>
>
> Many applications use that interface. I agree not to make deep changes for
> performance, but here the few changes are quite tiny, yet for a significant
> improvement, so aren't they worth it anyway ?
>
> Christophe

Well, TBH if anything, I'd prefer to worsen the performance to
actually discourage people from using sysfs for GPIOs. :)

It's not up to me though, so let's wait for Linus' opinion.

Thanks,
Bartosz

>
>
>>
>> The character device doesn't deal with strings so it will be much faster
>> anyway.
>>
>> Best regards,
>> Bartosz Golaszewski
>>
>

Re: [PATCH 1/4] gpio: sysfs: change 'value' attribute to prealloc

[Linus Walleij]

On Mon, Dec 18, 2017 at 11:08 AM, Christophe Leroy
<christophe.leroy@c-s.fr> wrote:

> 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>

I applied this because I don't want to waste honest development efforts.

Fixes and improvements I can accept. But not extensions.

But as Bartosz says it would be nice to focus efforts on the non-deprecated
ABI.

Yours,
Linus Walleij

Re: [PATCH 3/4] gpio: sysfs: don't use sprintf() for 'value' attribute

[Linus Walleij]

On Mon, Dec 18, 2017 at 11:08 AM, Christophe Leroy
<christophe.leroy@c-s.fr> wrote:

> A bench with 'perf record' shows that most of time spent in value_show()
> is spent in sprintf()
>
> --42.41%--sysfs_kf_read
>           |
>           |--39.73%--dev_attr_show
>           |          |
>           |          |--38.23%--value_show
>           |          |          |
>           |          |          |--29.22%--sprintf
>           |          |          |
>           |          |          |--2.94%--gpiod_get_value_cansleep
>           |          |          |
>
> value_show() only returns "0\n" or "1\n", therefore the use of
> sprintf() can be avoided
>
> With this patch we get the following result with 'perf record'
>
> --13.89%--sysfs_kf_read
>           |
>           |--10.72%--dev_attr_show
>           |          |
>           |          |--9.44%--value_show
>           |          |          |
>           |          |          |--4.61%--gpiod_get_value_cansleep
>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

Patch applied.

Yours,
Linus Walleij

Re: [PATCH 4/4] gpio: sysfs: avoid using kstrtol() in 'value' attribute write

[Linus Walleij]

On Mon, Dec 18, 2017 at 11:08 AM, Christophe Leroy
<christophe.leroy@c-s.fr> wrote:

> A 'perf record' on an app continuously writing in the 'value'
> attribute show that most of the time is spent in kstrtol()
>
> --17.99%--value_store
>           |
>           |--10.17%--kstrtoint
>           |          |
>           |          |--8.82%--kstrtoll
>           |
>           |--2.50%--gpiod_set_value_cansleep
>           |
>           |--1.82%--u16_gpio_set
>           |
>           |--1.46%--value_store
>
> The normal case is to write 0 or 1 in the attribute, therefore
> this patch avoids the call to kstrtol() in the most common cases
>
> Then 'perf record' shows
>
> --7.21%--value_store
>           |
>           |--2.69%--u16_gpio_set
>           |
>           |--1.47%--value_store
>           |
>           |--1.08%--gpiod_set_value_cansleep
>           |
>           |--0.60%--mutex_lock
>           |
>            --0.58%--mutex_unlock
>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

Patch applied.

Yours,
Linus Walleij