Re: [PATCH 2/2] rt: Increase/decrease the nr of migratory tasks when enabling/disabling migration

[Daniel Bristot de Oliveira]

On 06/22/2017 09:49 PM, Ingo Molnar wrote:
> So AFAICS it's this block that is used twice:
> 
>>>> +  rq = task_rq_lock(p, &rf);
>>>> +  p->nr_cpus_allowed = cpumask_weight(&p->cpus_mask);
>>>> +  if (unlikely((p->sched_class == &rt_sched_class ||
>>>> +                p->sched_class == &dl_sched_class) &&
>>>> +                p->nr_cpus_allowed > 1)) {
>>>> +          if (p->sched_class == &rt_sched_class)
>>>> +                  task_rq(p)->rt.rt_nr_migratory++;
>>>> +          else
>>>> +                  task_rq(p)->dl.dl_nr_migratory++;
>>>> +  }
>>>> +  task_rq_unlock(rq, p, &rf);
> or is there some difference I haven't noticed?

One block increases the number of migratory tasks, and the
other one decreases... 

How about this version? (if it is good, I will polish it in a v2).

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ce34e4f..0f66376 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7566,10 +7566,57 @@ const u32 sched_prio_to_wmult[40] = {
 
 #if defined(CONFIG_PREEMPT_COUNT) && defined(CONFIG_SMP)
 
+enum inc_dec_migratory {
+       DEC_NR_MIGRATORY = -1,
+       INC_NR_MIGRATORY = 1,
+};
+
+static inline void
+inc_dec_nr_migratory(struct task_struct *p, enum inc_dec_migratory id)
+{
+       if (unlikely((p->sched_class == &rt_sched_class ||
+                     p->sched_class == &dl_sched_class) &&
+                     p->nr_cpus_allowed > 1)) {
+               if (p->sched_class == &rt_sched_class)
+                       task_rq(p)->rt.rt_nr_migratory += id;
+               else
+                       task_rq(p)->dl.dl_nr_migratory += id;
+       }
+}
+
+static inline void
+migrate_disable_update_cpus_allowed(struct task_struct *p)
+{
+       struct rq *rq;
+       struct rq_flags rf;
+
+       p->cpus_ptr = cpumask_of(smp_processor_id());
+
+       rq = task_rq_lock(p, &rf);
+       inc_dec_nr_migratory(p, DEC_NR_MIGRATORY);
+       p->nr_cpus_allowed = 1;
+       task_rq_unlock(rq, p, &rf);
+}
+
+static inline void
+migrate_enable_update_cpus_allowed(struct task_struct *p)
+{
+       struct rq *rq;
+       struct rq_flags rf;
+
+       p->cpus_ptr = &p->cpus_mask;
+
+       rq = task_rq_lock(p, &rf);
+       p->nr_cpus_allowed = cpumask_weight(&p->cpus_mask);
+       inc_dec_nr_migratory(p, INC_NR_MIGRATORY);
+       task_rq_unlock(rq, p, &rf);
+}
+
 void migrate_disable(void)
 {
        struct task_struct *p = current;
 
+
        if (in_atomic() || irqs_disabled()) {
 #ifdef CONFIG_SCHED_DEBUG
                p->migrate_disable_atomic++;
@@ -7593,10 +7640,9 @@ void migrate_disable(void)
        preempt_disable();
        preempt_lazy_disable();
        pin_current_cpu();
-       p->migrate_disable = 1;
 
-       p->cpus_ptr = cpumask_of(smp_processor_id());
-       p->nr_cpus_allowed = 1;
+       migrate_disable_update_cpus_allowed(p);
+       p->migrate_disable = 1;
 
        preempt_enable();
 }
@@ -7606,6 +7652,7 @@ void migrate_enable(void)
 {
        struct task_struct *p = current;
 
+
        if (in_atomic() || irqs_disabled()) {
 #ifdef CONFIG_SCHED_DEBUG
                p->migrate_disable_atomic--;
@@ -7628,9 +7675,8 @@ void migrate_enable(void)
 
        preempt_disable();
 
-       p->cpus_ptr = &p->cpus_mask;
-       p->nr_cpus_allowed = cpumask_weight(&p->cpus_mask);
        p->migrate_disable = 0;
+       migrate_enable_update_cpus_allowed(p);
 
        if (p->migrate_disable_update) {
                struct rq *rq;