sched: fix SMP migration latencies

fix SMP migration latencies: the vruntimes of different CPUs are
at incompatible offsets so they have to be fixed up when migrating
a task across CPUs.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

kernel/sched.c

@@ -992,6 +992,9 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
 	if (p->se.block_start)
 		p->se.block_start -= clock_offset;
 #endif
+	if (likely(new_rq->cfs.min_vruntime))
+		p->se.vruntime -= old_rq->cfs.min_vruntime -
+						new_rq->cfs.min_vruntime;
 
 	__set_task_cpu(p, new_cpu);
 }