sched: Improve readability in update_cpu_load() code

PATCH In review Gautham R Shenoy 3 participants 6 messages May 15, 2008

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Gautham R Shenoy

author

2008-05-15 13:03 UTC #0 lore raw

PATCH 1/1 sched: Improve readability in update_cpu_load() code

Author: Gautham R Shenoy <[email protected]>
Date:   Thu May 15 17:55:49 2008 +0530

sched: Improve readability in update_cpu_load() code

Currently the cpu_load[i] is calculated as:
this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;

However, since scale = 2^i, this can be simplified as:
this_rq->cpu_load[i] = old_load + ((new_load - old_load) >> i);

Makes it easier to read.

Signed-off-by Gautham R Shenoy <[email protected]>

kernel/sched.c +1 -1

index 2d7d8f1..e1a6985 100644
@@ -2921,7 +2921,7 @@ static void update_cpu_load(struct rq *this_rq)
 		 */
 		if (new_load > old_load)
 			new_load += scale-1;
-		this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;
+		this_rq->cpu_load[i] = old_load + ((new_load - old_load) >> i);
 	}
 }

Signature · 2 lines

Thanks and Regards
gautham

Srivatsa Vaddagiri

2008-05-15 14:43 UTC #1 lore raw

Quoted 19 lines · Gautham R Shenoy

Author: Gautham R Shenoy <[email protected]>
Date:   Thu May 15 17:55:49 2008 +0530
sched: Improve readability in update_cpu_load() code
Currently the cpu_load[i] is calculated as:
this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;
However, since scale = 2^i, this can be simplified as:
this_rq->cpu_load[i] = old_load + ((new_load - old_load) >> i);
Makes it easier to read.
Signed-off-by Gautham R Shenoy <[email protected]>
kernel/sched.c +0 -0
index 2d7d8f1..e1a6985 100644

kernel/sched.c static void update_cpu_load(struct rq *this_rq) · line 2924

Quoted 5 lines

kernel/sched.c +1 -1

@@ -2921,7 +2921,7 @@ static void update_cpu_load(struct rq *this_rq)
 		 */
 		if (new_load > old_load)
 			new_load += scale-1;
-		this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;
+		this_rq->cpu_load[i] = old_load + ((new_load - old_load) >> i);

This wont work when new_load < old_load ..

For ex: I tried this prog:

#include <stdio.h>

main()

{
	unsigned long old_load = 100, new_load = 90, this_load, this_load1;
	int i = 1, scale = 2 << i;

	this_load = (old_load*(scale-1) + new_load) >> i;
	this_load1 = old_load + ((new_load - old_load) >> i);

	printf ("this_load = %u, this_load1 = %u \n", this_load, this_load1);
}

This is what I get:

$ ./a.out
this_load = 195, this_load1 = 2147483743
$

Signature · 2 lines

Regards,
vatsa

Srivatsa Vaddagiri

2008-05-15 14:53 UTC #2 lore raw

Quoted 10 lines · Srivatsa Vaddagiri

This wont work when new_load < old_load ..
For ex: I tried this prog:
#include <stdio.h>
main()
{
	unsigned long old_load = 100, new_load = 90, this_load, this_load1;
	int i = 1, scale = 2 << i;

s/scale = 2<< i/scale = 2 << (i-1)

Quoted 7 lines

	this_load = (old_load*(scale-1) + new_load) >> i;
	this_load1 = old_load + ((new_load - old_load) >> i);

	printf ("this_load = %u, this_load1 = %u \n", this_load, this_load1);
}

Quoted 5 lines

This is what I get:

$ ./a.out
this_load = 195, this_load1 = 2147483743
$

[with above modification:]

this_load = 95, this_load1 = 2147483743

Signature · 2 lines

Regards,
vatsa

Dmitry Adamushko

2008-05-15 15:16 UTC #3 lore raw

In reply to Srivatsa Vaddagiri

2008/5/15 Srivatsa Vaddagiri <[email protected]>:

Quoted 32 lines · Gautham R Shenoy

Quoted 19 lines
Author: Gautham R Shenoy <[email protected]>
Date:   Thu May 15 17:55:49 2008 +0530
sched: Improve readability in update_cpu_load() code
Currently the cpu_load[i] is calculated as:
this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;
However, since scale = 2^i, this can be simplified as:
this_rq->cpu_load[i] = old_load + ((new_load - old_load) >> i);
Makes it easier to read.
Signed-off-by Gautham R Shenoy <[email protected]>
kernel/sched.c +0 -0
index 2d7d8f1..e1a6985 100644
kernel/sched.c static void update_cpu_load(struct rq *this_rq) · line 2924
Quoted 5 lines
kernel/sched.c +1 -1
@@ -2921,7 +2921,7 @@ static void update_cpu_load(struct rq *this_rq)
               */
              if (new_load > old_load)
                      new_load += scale-1;
-             this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;
+             this_rq->cpu_load[i] = old_load + ((new_load - old_load) >> i);
This wont work when new_load < old_load ..
For ex: I tried this prog:
#include <stdio.h>

Quoted 7 lines

main()

{
       unsigned long old_load = 100, new_load = 90, this_load, this_load1;
       int i = 1, scale = 2 << i;

       this_load = (old_load*(scale-1) + new_load) >> i;
       this_load1 = old_load + ((new_load - old_load) >> i);

it should be

this_load2 = 2 * old_load + (new_load >> i) - (old_load >> i);

scale == 2 << i == 1 << (i + 1), so scale >> i = 2.

and it may result in (probably) little difefrences due to different rounding. I think, for me the currently existing version is more easy-to-read.

Quoted 3 lines

--
Regards,
vatsa

Signature · 2 lines

Best regards,
Dmitry Adamushko

Dmitry Adamushko

2008-05-15 15:32 UTC #4 lore raw

2008/5/15 Dmitry Adamushko <[email protected]>:

Quoted 38 lines

2008/5/15 Srivatsa Vaddagiri <[email protected]>:
Quoted 37 lines · Gautham R Shenoy
Quoted 19 lines
Author: Gautham R Shenoy <[email protected]>
Date:   Thu May 15 17:55:49 2008 +0530
sched: Improve readability in update_cpu_load() code
Currently the cpu_load[i] is calculated as:
this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;
However, since scale = 2^i, this can be simplified as:
this_rq->cpu_load[i] = old_load + ((new_load - old_load) >> i);
Makes it easier to read.
Signed-off-by Gautham R Shenoy <[email protected]>
kernel/sched.c +0 -0
index 2d7d8f1..e1a6985 100644
kernel/sched.c static void update_cpu_load(struct rq *this_rq) · line 2924
Quoted 5 lines
kernel/sched.c +1 -1
@@ -2921,7 +2921,7 @@ static void update_cpu_load(struct rq *this_rq)
               */
              if (new_load > old_load)
                      new_load += scale-1;
-             this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;
+             this_rq->cpu_load[i] = old_load + ((new_load - old_load) >> i);
This wont work when new_load < old_load ..
For ex: I tried this prog:
#include <stdio.h>
main()
{
       unsigned long old_load = 100, new_load = 90, this_load, this_load1;
       int i = 1, scale = 2 << i;

Quoted 8 lines

Quoted 2 lines
       this_load = (old_load*(scale-1) + new_load) >> i;
       this_load1 = old_load + ((new_load - old_load) >> i);
it should be
this_load2 = 2 * old_load + (new_load >> i) - (old_load >> i);
scale == 2 << i == 1 << (i + 1), so scale >> i = 2.

argh.. sorry, it's (scale = 2 << i) in your test-program which is wrong. 2^i == (1 << i), so the (2 *) part is redundant, of course.

this_load2 = old_load + (new_load >> i) - (old_load >> i);

Signature · 2 lines

Best regards,
Dmitry Adamushko

Gautham R Shenoy

author

2008-05-15 17:10 UTC #5 lore raw

In reply to Srivatsa Vaddagiri

Quoted 15 lines · Srivatsa Vaddagiri

Quoted 14 lines · Gautham R Shenoy
Author: Gautham R Shenoy <[email protected]>
Date:   Thu May 15 17:55:49 2008 +0530
sched: Improve readability in update_cpu_load() code
Currently the cpu_load[i] is calculated as:
this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;
However, since scale = 2^i, this can be simplified as:
this_rq->cpu_load[i] = old_load + ((new_load - old_load) >> i);
Makes it easier to read.
Signed-off-by Gautham R Shenoy <[email protected]>

Quoted 13 lines

kernel/sched.c static void update_cpu_load(struct rq *this_rq) · line 2924
Quoted 10 lines
kernel/sched.c +1 -1
index 2d7d8f1..e1a6985 100644
@@ -2921,7 +2921,7 @@ static void update_cpu_load(struct rq *this_rq)
 		 */
 		if (new_load > old_load)
 			new_load += scale-1;
-		this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;
+		this_rq->cpu_load[i] = old_load + ((new_load - old_load) >> i);
This wont work when new_load < old_load ..

Sorry for the noise. I must have read the previous if() condition incorrectly.

Quoted 26 lines

For ex: I tried this prog:

#include <stdio.h>

main()

{
	unsigned long old_load = 100, new_load = 90, this_load, this_load1;
	int i = 1, scale = 2 << i;

	this_load = (old_load*(scale-1) + new_load) >> i;
	this_load1 = old_load + ((new_load - old_load) >> i);

	printf ("this_load = %u, this_load1 = %u \n", this_load, this_load1);
}

This is what I get:

$ ./a.out
this_load = 195, this_load1 = 2147483743
$

Signature · 2 lines

Regards,
vatsa

Signature · 2 lines

Thanks and Regards
gautham