sched/fair: Replace source_load() & target_load() with weighted_cpuload() [Linux 5.3]

This Linux kernel change "sched/fair: Replace source_load() & target_load() with weighted_cpuload()" is included in the Linux 5.3 release. This change is authored by Dietmar Eggemann <dietmar.eggemann [at] arm.com> on Mon May 27 07:21:11 2019 +0100. The commit for this change in Linux stable tree is 1c1b8a7 (patch).

sched/fair: Replace source_load() & target_load() with weighted_cpuload()

With LB_BIAS disabled, source_load() & target_load() return
weighted_cpuload(). Replace both with calls to weighted_cpuload().

The function to obtain the load index (sd->*_idx) for an sd,
get_sd_load_idx(), can be removed as well.

Finally, get rid of the sched feature LB_BIAS.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Rik van Riel <riel@surriel.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Perret <quentin.perret@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20190527062116.11512-3-dietmar.eggemann@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

There are 91 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 kernel/sched/fair.c     | 90 +++----------------------------------------------
 kernel/sched/features.h |  1 -
 2 files changed, 4 insertions(+), 87 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1aab323f..5b9691e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1467,8 +1467,6 @@ bool should_numa_migrate_memory(struct task_struct *p, struct page * page,
 }

 static unsigned long weighted_cpuload(struct rq *rq);
-static unsigned long source_load(int cpu, int type);
-static unsigned long target_load(int cpu, int type);

 /* Cached statistics for all CPUs within a node */
 struct numa_stats {
@@ -5333,45 +5331,11 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)

 #endif /* CONFIG_NO_HZ_COMMON */

-/* Used instead of source_load when we know the type == 0 */
 static unsigned long weighted_cpuload(struct rq *rq)
 {
    return cfs_rq_runnable_load_avg(&rq->cfs);
 }

-/*
- * Return a low guess at the load of a migration-source CPU weighted
- * according to the scheduling class and "nice" value.
- *
- * We want to under-estimate the load of migration sources, to
- * balance conservatively.
- */
-static unsigned long source_load(int cpu, int type)
-{
-   struct rq *rq = cpu_rq(cpu);
-   unsigned long total = weighted_cpuload(rq);
-
-   if (type == 0 || !sched_feat(LB_BIAS))
-       return total;
-
-   return min(rq->cpu_load[type-1], total);
-}
-
-/*
- * Return a high guess at the load of a migration-target CPU weighted
- * according to the scheduling class and "nice" value.
- */
-static unsigned long target_load(int cpu, int type)
-{
-   struct rq *rq = cpu_rq(cpu);
-   unsigned long total = weighted_cpuload(rq);
-
-   if (type == 0 || !sched_feat(LB_BIAS))
-       return total;
-
-   return max(rq->cpu_load[type-1], total);
-}
-
 static unsigned long capacity_of(int cpu)
 {
    return cpu_rq(cpu)->cpu_capacity;
@@ -5479,7 +5443,7 @@ static int wake_wide(struct task_struct *p)
    s64 this_eff_load, prev_eff_load;
    unsigned long task_load;

-   this_eff_load = target_load(this_cpu, sd->wake_idx);
+   this_eff_load = weighted_cpuload(cpu_rq(this_cpu));

    if (sync) {
        unsigned long current_load = task_h_load(current);
@@ -5497,7 +5461,7 @@ static int wake_wide(struct task_struct *p)
        this_eff_load *= 100;
    this_eff_load *= capacity_of(prev_cpu);

-   prev_eff_load = source_load(prev_cpu, sd->wake_idx);
+   prev_eff_load = weighted_cpuload(cpu_rq(prev_cpu));
    prev_eff_load -= task_load;
    if (sched_feat(WA_BIAS))
        prev_eff_load *= 100 + (sd->imbalance_pct - 100) / 2;
@@ -5558,14 +5522,10 @@ static unsigned long capacity_spare_without(int cpu, struct task_struct *p)
    unsigned long this_runnable_load = ULONG_MAX;
    unsigned long min_avg_load = ULONG_MAX, this_avg_load = ULONG_MAX;
    unsigned long most_spare = 0, this_spare = 0;
-   int load_idx = sd->forkexec_idx;
    int imbalance_scale = 100 + (sd->imbalance_pct-100)/2;
    unsigned long imbalance = scale_load_down(NICE_0_LOAD) *
                (sd->imbalance_pct-100) / 100;

-   if (sd_flag & SD_BALANCE_WAKE)
-       load_idx = sd->wake_idx;
-
    do {
        unsigned long load, avg_load, runnable_load;
        unsigned long spare_cap, max_spare_cap;
@@ -5589,12 +5549,7 @@ static unsigned long capacity_spare_without(int cpu, struct task_struct *p)
        max_spare_cap = 0;

        for_each_cpu(i, sched_group_span(group)) {
-           /* Bias balancing toward CPUs of our domain */
-           if (local_group)
-               load = source_load(i, load_idx);
-           else
-               load = target_load(i, load_idx);
-
+           load = weighted_cpuload(cpu_rq(i));
            runnable_load += load;

            avg_load += cfs_rq_load_avg(&cpu_rq(i)->cfs);
@@ -7676,34 +7631,6 @@ static inline void init_sd_lb_stats(struct sd_lb_stats *sds)
    };
 }

-/**
- * get_sd_load_idx - Obtain the load index for a given sched domain.
- * @sd: The sched_domain whose load_idx is to be obtained.
- * @idle: The idle status of the CPU for whose sd load_idx is obtained.
- *
- * Return: The load index.
- */
-static inline int get_sd_load_idx(struct sched_domain *sd,
-                   enum cpu_idle_type idle)
-{
-   int load_idx;
-
-   switch (idle) {
-   case CPU_NOT_IDLE:
-       load_idx = sd->busy_idx;
-       break;
-
-   case CPU_NEWLY_IDLE:
-       load_idx = sd->newidle_idx;
-       break;
-   default:
-       load_idx = sd->idle_idx;
-       break;
-   }
-
-   return load_idx;
-}
-
 static unsigned long scale_rt_capacity(struct sched_domain *sd, int cpu)
 {
    struct rq *rq = cpu_rq(cpu);
@@ -7992,9 +7919,6 @@ static inline void update_sg_lb_stats(struct lb_env *env,
                      struct sg_lb_stats *sgs,
                      int *sg_status)
 {
-   int local_group = cpumask_test_cpu(env->dst_cpu, sched_group_span(group));
-   int load_idx = get_sd_load_idx(env->sd, env->idle);
-   unsigned long load;
    int i, nr_running;

    memset(sgs, 0, sizeof(*sgs));
@@ -8005,13 +7929,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
        if ((env->flags & LBF_NOHZ_STATS) && update_nohz_stats(rq, false))
            env->flags |= LBF_NOHZ_AGAIN;

-       /* Bias balancing toward CPUs of our domain: */
-       if (local_group)
-           load = target_load(i, load_idx);
-       else
-           load = source_load(i, load_idx);
-
-       sgs->group_load += load;
+       sgs->group_load += weighted_cpuload(rq);
        sgs->group_util += cpu_util(i);
        sgs->sum_nr_running += rq->cfs.h_nr_running;

diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index 858589b..2410db5 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -39,7 +39,6 @@

 SCHED_FEAT(HRTICK, false)
 SCHED_FEAT(DOUBLE_TICK, false)
-SCHED_FEAT(LB_BIAS, false)

 /*
  * Decrement CPU capacity based on time not spent running tasks

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