sched: Add an rq migration call-back to sched_class

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: migrate_task_rq(struct task_struct *p, int next_cpu)

(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>
Reviewed-by: Ben Segall <bsegall@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20120823141506.660023400@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 14 insertions, 0 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 00898f1fb69..f26860074ef 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -952,6 +952,8 @@ 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 83194175e84..5e602e6ba0c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3047,6 +3047,17 @@ 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 the state of rq->lock, should be made.
+ */
+static void
+migrate_task_rq_fair(struct task_struct *p, int next_cpu)
+{
+}
 #endif /* CONFIG_SMP */
 
 static unsigned long
@@ -5607,6 +5618,7 @@ 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,