hello wanpeng,
On Mon, Sep 07, 2015 at 05:45:20PM +0800, Wanpeng Li wrote:
> The sleeper task will be normalized when moved from fair_sched_class, in
> order that vruntime will be adjusted either the task is running or sleeping
> when moved back. The nomalization in switch_to_fair for sleep task will
> result in lose fair sleeper bonus in place_entity() once the vruntime -
> cfs_rq->min_vruntime is big when moved from fair_sched_class.
it is nothing to do with normalization.
if vruntime - cfs_rq->min_vruntime is big even though place_entity() was
called when moved from fair class, then we actually expect that it still has
a big vruntime when moved back to fair class.
if we don't expect that it still has a big vruntime when moved back to fair
class, we need to consider other approaches e.g. to move a position calling
place_entity() or to add place_entity() call properly ..
however we should not touch normalization logic. in other words, if we
normalized the vruntime when leaved, then we should necessarily restore the
vruntime to a non-normalized value when moved back.
>
> This patch fix it by adjusting vruntime just during migrating as original
> codes since the vruntime of the task has usually NOT been normalized in
> this case.
could you explain this in detail? when is a vruntime not normalized?
thanks,
byungchul
>
> Signed-off-by: Wanpeng Li <wanpeng...@hotmail.com>
> ---
> kernel/sched/fair.c | 11 +++++++----
> 1 files changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d26d3b7..eb9aa35 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8005,9 +8005,6 @@ static void attach_task_cfs_rq(struct task_struct *p)
>
> /* Synchronize task with its cfs_rq */
> attach_entity_load_avg(cfs_rq, se);
> -
> - if (!vruntime_normalized(p))
> - se->vruntime += cfs_rq->min_vruntime;
> }
>
> static void switched_from_fair(struct rq *rq, struct task_struct *p)
> @@ -8066,14 +8063,20 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
> #ifdef CONFIG_FAIR_GROUP_SCHED
> static void task_move_group_fair(struct task_struct *p)
> {
> + struct sched_entity *se = &p->se;
> + struct cfs_rq *cfs_rq = cfs_rq_of(se);
> +
> detach_task_cfs_rq(p);
> set_task_rq(p, task_cpu(p));
>
> #ifdef CONFIG_SMP
> /* Tell se's cfs_rq has been changed -- migrated */
> - p->se.avg.last_update_time = 0;
> + se->avg.last_update_time = 0;
> #endif
> attach_task_cfs_rq(p);
> +
> + if (!vruntime_normalized(p))
> + se->vruntime += cfs_rq->min_vruntime;
> }
>
> void free_fair_sched_group(struct task_group *tg)
> --
> 1.7.1
>
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