[PATCH] sched/fair: Fix load_above_capacity fixed point arithmetic width

[PATCH] sched/fair: Fix load_above_capacity fixed point arithmetic width

[Dietmar Eggemann]

Since commit 2159197d6677 ("sched/core: Enable increased load resolution
on 64-bit kernels") we now have two different fixed point units for
load.
load_above_capacity has to have 10 bit fixed point unit like PELT
whereas NICE_0_LOAD has 20 bit fixed point unit on 64-bit kernels.
Fix this by scaling down NICE_0_LOAD when multiplying
load_above_capacity with it.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Acked-by: Morten Rasmussen <morten.rasmussen@arm.com>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4088eedea763..fe4093807852 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7147,7 +7147,7 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
 		load_above_capacity = busiest->sum_nr_running * SCHED_CAPACITY_SCALE;
 		if (load_above_capacity > busiest->group_capacity) {
 			load_above_capacity -= busiest->group_capacity;
-			load_above_capacity *= NICE_0_LOAD;
+			load_above_capacity *= scale_load_down(NICE_0_LOAD);
 			load_above_capacity /= busiest->group_capacity;
 		} else
 			load_above_capacity = ~0UL;
-- 
1.9.1

Re: [PATCH] sched/fair: Fix load_above_capacity fixed point arithmetic width

[Vincent Guittot]

On 10 August 2016 at 12:27, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
> Since commit 2159197d6677 ("sched/core: Enable increased load resolution
> on 64-bit kernels") we now have two different fixed point units for
> load.
> load_above_capacity has to have 10 bit fixed point unit like PELT
> whereas NICE_0_LOAD has 20 bit fixed point unit on 64-bit kernels.
> Fix this by scaling down NICE_0_LOAD when multiplying
> load_above_capacity with it.
>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Acked-by: Morten Rasmussen <morten.rasmussen@arm.com>
> ---
>  kernel/sched/fair.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 4088eedea763..fe4093807852 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7147,7 +7147,7 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
>                 load_above_capacity = busiest->sum_nr_running * SCHED_CAPACITY_SCALE;
>                 if (load_above_capacity > busiest->group_capacity) {
>                         load_above_capacity -= busiest->group_capacity;
> -                       load_above_capacity *= NICE_0_LOAD;
> +                       load_above_capacity *= scale_load_down(NICE_0_LOAD);

FWIW, Acked-by: Vincent Guittot <vincent.guittot@linaro.org>

>                         load_above_capacity /= busiest->group_capacity;
>                 } else
>                         load_above_capacity = ~0UL;
> --
> 1.9.1
>

[tip:sched/core] sched/fair: Fix load_above_capacity fixed point arithmetic width

[tip-bot for Dietmar Eggemann]

Commit-ID:  2665621506e178a1f62e59200403c359c463ea5e
Gitweb:     http://git.kernel.org/tip/2665621506e178a1f62e59200403c359c463ea5e
Author:     Dietmar Eggemann <dietmar.eggemann@arm.com>
AuthorDate: Wed, 10 Aug 2016 11:27:27 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 5 Sep 2016 13:29:44 +0200

sched/fair: Fix load_above_capacity fixed point arithmetic width

Since commit:

  2159197d6677 ("sched/core: Enable increased load resolution on 64-bit kernels")

we now have two different fixed point units for load.

load_above_capacity has to have 10 bits fixed point unit like PELT,
whereas NICE_0_LOAD has 20 bit fixed point unit on 64-bit kernels.

Fix this by scaling down NICE_0_LOAD when multiplying
load_above_capacity with it.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
Acked-by: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yuyang Du <yuyang.du@intel.com>
Link: http://lkml.kernel.org/r/1470824847-5316-1-git-send-email-dietmar.eggemann@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9a18aae..6011bfe 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7193,7 +7193,7 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
 		load_above_capacity = busiest->sum_nr_running * SCHED_CAPACITY_SCALE;
 		if (load_above_capacity > busiest->group_capacity) {
 			load_above_capacity -= busiest->group_capacity;
-			load_above_capacity *= NICE_0_LOAD;
+			load_above_capacity *= scale_load_down(NICE_0_LOAD);
 			load_above_capacity /= busiest->group_capacity;
 		} else
 			load_above_capacity = ~0UL;