[PATCH 0/2] Refactor some codes in sched/pelt.c

[PATCH 0/2] Refactor some codes in sched/pelt.c

[Tang Yizhou]

After reading the implementation of PELT, I try to refactor it as
below.

Tang Yizhou (2):
  sched/pelt: Remove redundant variable in __accumulate_pelt_segments
  sched/pelt: Change the type of parameter running to bool

 kernel/sched/pelt.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

-- 
2.17.1

[PATCH 1/2] sched/pelt: Remove redundant variable in __accumulate_pelt_segments

[Tang Yizhou]

As the comment of function accumulate_sum() describes the equation clearly,
There is no need to use a redundant variable c3. Let's make a comment for
d3 directly.

Signed-off-by: Tang Yizhou <tangyizhou@huawei.com>
---
 kernel/sched/pelt.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
index a554e3bbab2b..3584df2a0b8e 100644
--- a/kernel/sched/pelt.c
+++ b/kernel/sched/pelt.c
@@ -60,7 +60,7 @@ static u64 decay_load(u64 val, u64 n)
 
 static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3)
 {
-	u32 c1, c2, c3 = d3; /* y^0 == 1 */
+	u32 c1, c2;
 
 	/*
 	 * c1 = d1 y^p
@@ -78,7 +78,7 @@ static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3)
 	 */
 	c2 = LOAD_AVG_MAX - decay_load(LOAD_AVG_MAX, periods) - 1024;
 
-	return c1 + c2 + c3;
+	return c1 + c2 + d3;  /* d3: y^0 == 1 */
 }
 
 /*
-- 
2.17.1

[PATCH 2/2] sched/pelt: Change the type of parameter running to bool

[Tang Yizhou]

Parameter 'running' in function ___update_load_sum() and
accumulate_sum() describes whether an se is running or not, so change
the type of it to bool to make the code more readable.

Signed-off-by: Tang Yizhou <tangyizhou@huawei.com>
---
 kernel/sched/pelt.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
index 3584df2a0b8e..2010b3bd6e49 100644
--- a/kernel/sched/pelt.c
+++ b/kernel/sched/pelt.c
@@ -104,7 +104,7 @@ static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3)
  */
 static __always_inline u32
 accumulate_sum(u64 delta, struct sched_avg *sa,
-	       unsigned long load, unsigned long runnable, int running)
+	       unsigned long load, unsigned long runnable, bool running)
 {
 	u32 contrib = (u32)delta; /* p == 0 -> delta < 1024 */
 	u64 periods;
@@ -182,7 +182,7 @@ accumulate_sum(u64 delta, struct sched_avg *sa,
  */
 static __always_inline int
 ___update_load_sum(u64 now, struct sched_avg *sa,
-		  unsigned long load, unsigned long runnable, int running)
+		  unsigned long load, unsigned long runnable, bool running)
 {
 	u64 delta;
 
-- 
2.17.1

Re: [PATCH 1/2] sched/pelt: Remove redundant variable in __accumulate_pelt_segments

[Peter Zijlstra]

On Thu, Nov 25, 2021 at 11:00:18AM +0800, Tang Yizhou wrote:
> As the comment of function accumulate_sum() describes the equation clearly,
> There is no need to use a redundant variable c3. Let's make a comment for
> d3 directly.

Why bother? Surely the compiler is clever enough to figure out the same
and avoid instantiating the variable. All you've done is made the code
less obvious.

Re: [PATCH 2/2] sched/pelt: Change the type of parameter running to bool

[Peter Zijlstra]

On Thu, Nov 25, 2021 at 11:00:19AM +0800, Tang Yizhou wrote:
> Parameter 'running' in function ___update_load_sum() and
> accumulate_sum() describes whether an se is running or not, so change
> the type of it to bool to make the code more readable.
> 
> Signed-off-by: Tang Yizhou <tangyizhou@huawei.com>
> ---
>  kernel/sched/pelt.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
> index 3584df2a0b8e..2010b3bd6e49 100644
> --- a/kernel/sched/pelt.c
> +++ b/kernel/sched/pelt.c
> @@ -104,7 +104,7 @@ static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3)
>   */
>  static __always_inline u32
>  accumulate_sum(u64 delta, struct sched_avg *sa,
> -	       unsigned long load, unsigned long runnable, int running)
> +	       unsigned long load, unsigned long runnable, bool running)
>  {
>  	u32 contrib = (u32)delta; /* p == 0 -> delta < 1024 */
>  	u64 periods;
> @@ -182,7 +182,7 @@ accumulate_sum(u64 delta, struct sched_avg *sa,
>   */
>  static __always_inline int
>  ___update_load_sum(u64 now, struct sched_avg *sa,
> -		  unsigned long load, unsigned long runnable, int running)
> +		  unsigned long load, unsigned long runnable, bool running)
>  {
>  	u64 delta;

And this function has:

	runnable = running = 0;

and then people complain about assigning 0 to _Bool, and then we get
idiocy like:

	runnable = running = false;

Please...

Re: [PATCH 2/2] sched/pelt: Change the type of parameter running to bool

[Tang Yizhou]

On 2021/11/25 17:55, Peter Zijlstra wrote:
> On Thu, Nov 25, 2021 at 11:00:19AM +0800, Tang Yizhou wrote:
>> Parameter 'running' in function ___update_load_sum() and
>> accumulate_sum() describes whether an se is running or not, so change
>> the type of it to bool to make the code more readable.
>>
>> Signed-off-by: Tang Yizhou <tangyizhou@huawei.com>
>> ---
>>  kernel/sched/pelt.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
>> index 3584df2a0b8e..2010b3bd6e49 100644
>> --- a/kernel/sched/pelt.c
>> +++ b/kernel/sched/pelt.c
>> @@ -104,7 +104,7 @@ static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3)
>>   */
>>  static __always_inline u32
>>  accumulate_sum(u64 delta, struct sched_avg *sa,
>> -	       unsigned long load, unsigned long runnable, int running)
>> +	       unsigned long load, unsigned long runnable, bool running)
>>  {
>>  	u32 contrib = (u32)delta; /* p == 0 -> delta < 1024 */
>>  	u64 periods;
>> @@ -182,7 +182,7 @@ accumulate_sum(u64 delta, struct sched_avg *sa,
>>   */
>>  static __always_inline int
>>  ___update_load_sum(u64 now, struct sched_avg *sa,
>> -		  unsigned long load, unsigned long runnable, int running)
>> +		  unsigned long load, unsigned long runnable, bool running)
>>  {
>>  	u64 delta;
> 
> And this function has:
> 
> 	runnable = running = 0;
> 
> and then people complain about assigning 0 to _Bool, and then we get
> idiocy like:
> 
> 	runnable = running = false;

How about:
        running = runnable = 0;

> 
> Please...
> .
> 

Thanks,
Tang

Re: [PATCH 2/2] sched/pelt: Change the type of parameter running to bool

[Tang Yizhou]

On 2021/11/25 17:55, Peter Zijlstra wrote:
> On Thu, Nov 25, 2021 at 11:00:19AM +0800, Tang Yizhou wrote:
>> Parameter 'running' in function ___update_load_sum() and
>> accumulate_sum() describes whether an se is running or not, so change
>> the type of it to bool to make the code more readable.
>>
>> Signed-off-by: Tang Yizhou <tangyizhou@huawei.com>
>> ---
>>  kernel/sched/pelt.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
>> index 3584df2a0b8e..2010b3bd6e49 100644
>> --- a/kernel/sched/pelt.c
>> +++ b/kernel/sched/pelt.c
>> @@ -104,7 +104,7 @@ static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3)
>>   */
>>  static __always_inline u32
>>  accumulate_sum(u64 delta, struct sched_avg *sa,
>> -	       unsigned long load, unsigned long runnable, int running)
>> +	       unsigned long load, unsigned long runnable, bool running)
>>  {
>>  	u32 contrib = (u32)delta; /* p == 0 -> delta < 1024 */
>>  	u64 periods;
>> @@ -182,7 +182,7 @@ accumulate_sum(u64 delta, struct sched_avg *sa,
>>   */
>>  static __always_inline int
>>  ___update_load_sum(u64 now, struct sched_avg *sa,
>> -		  unsigned long load, unsigned long runnable, int running)
>> +		  unsigned long load, unsigned long runnable, bool running)
>>  {
>>  	u64 delta;
> 
> And this function has:
> 
> 	runnable = running = 0;
> 
> and then people complain about assigning 0 to _Bool, and then we get
> idiocy like:
> 
> 	runnable = running = false;
> 
> Please...
> .
> 

I see, assigning 0 to _Bool is inappropriate.
Thanks for your review.