From 7855a35ac07a350e2cd26f09568a6d8e372be358 Mon Sep 17 00:00:00 2001 From: Byungchul Park Date: Mon, 10 Aug 2015 18:02:55 +0900 Subject: [PATCH] sched: Ensure a task has a non-normalized vruntime when returning back to CFS Current code ensures that a task has a normalized vruntime when switching away from the fair class, but it does not ensure the task has a non-normalized vruntime when switching back to the fair class. This is an example breaking this consistency: 1. a task is in fair class and !queued 2. changes its class to RT class (still !queued) 3. changes its class to fair class again (still !queued) Signed-off-by: Byungchul Park Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1439197375-27927-1-git-send-email-byungchul.park@lge.com Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 858b94ab1bd2..f0950fde1f5b 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7930,16 +7930,31 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p) */ static void switched_to_fair(struct rq *rq, struct task_struct *p) { -#ifdef CONFIG_FAIR_GROUP_SCHED struct sched_entity *se = &p->se; + +#ifdef CONFIG_FAIR_GROUP_SCHED /* * Since the real-depth could have been changed (only FAIR * class maintain depth value), reset depth properly. */ se->depth = se->parent ? se->parent->depth + 1 : 0; #endif - if (!task_on_rq_queued(p)) + + if (!task_on_rq_queued(p)) { + + /* + * Ensure the task has a non-normalized vruntime when it is switched + * back to the fair class with !queued, so that enqueue_entity() at + * wake-up time will do the right thing. + * + * If it's queued, then the enqueue_entity(.flags=0) makes the task + * has non-normalized vruntime, if it's !queued, then it still has + * normalized vruntime. + */ + if (p->state != TASK_RUNNING) + se->vruntime += cfs_rq_of(se)->min_vruntime; return; + } /* * We were most likely switched from sched_rt, so