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Subject[PATCH 05/16] sched: add an rq migration call-back to sched_class
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Since we are now doing bottom up load accumulation we need explicit
notification when a task has been re-parented so that the old hierarchy can be
updated.

Adds task_migrate_rq(struct rq *prev, struct *rq new_rq);

(The alternative is to do this out of __set_task_cpu, but it was suggested that
this would be a cleaner encapsulation.)

Signed-off-by: Paul Turner <pjt@google.com>
---
include/linux/sched.h | 1 +
kernel/sched/core.c | 2 ++
kernel/sched/fair.c | 12 ++++++++++++
3 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 842c4df..fdfdfab 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1102,6 +1102,7 @@ struct sched_class {

#ifdef CONFIG_SMP
int (*select_task_rq)(struct task_struct *p, int sd_flag, int flags);
+ void (*migrate_task_rq)(struct task_struct *p, int next_cpu);

void (*pre_schedule) (struct rq *this_rq, struct task_struct *task);
void (*post_schedule) (struct rq *this_rq);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index aeb8e56..c3686eb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1109,6 +1109,8 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
trace_sched_migrate_task(p, new_cpu);

if (task_cpu(p) != new_cpu) {
+ if (p->sched_class->migrate_task_rq)
+ p->sched_class->migrate_task_rq(p, new_cpu);
p->se.nr_migrations++;
perf_sw_event(PERF_COUNT_SW_CPU_MIGRATIONS, 1, NULL, 0);
}
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6200d20..33f582a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3089,6 +3089,17 @@ unlock:

return new_cpu;
}
+
+/*
+ * Called immediately before a task is migrated to a new cpu; task_cpu(p) and
+ * cfs_rq_of(p) references at time of call are still valid and identify the
+ * previous cpu. However, the caller only guarantees p->pi_lock is held; no
+ * other assumptions, including rq->lock state, should be made.
+ * Caller guarantees p->pi_lock held, but nothing else.
+ */
+static void
+migrate_task_rq_fair(struct task_struct *p, int next_cpu) {
+}
#endif /* CONFIG_SMP */

static unsigned long
@@ -5754,6 +5765,7 @@ const struct sched_class fair_sched_class = {

#ifdef CONFIG_SMP
.select_task_rq = select_task_rq_fair,
+ .migrate_task_rq = migrate_task_rq_fair,

.rq_online = rq_online_fair,
.rq_offline = rq_offline_fair,



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