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SubjectRe: [PATCH] sched/fair: fix vruntime_normalized for remote non-migration wakeup
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On 08/31/2018 03:42 PM, Steve Muckle wrote:
> When a task which previously ran on a given CPU is remotely queued to
> wake up on that same CPU, there is a period where the task's state is
> TASK_WAKING and its vruntime is not normalized. This is not accounted
> for in vruntime_normalized() which will cause an
> error in the task's vruntime if it is switched from the fair class
> during this time, for example if it is boosted to RT priority via
> rt_mutex_setprio. The rq's min_vruntime will not be subtracted from the
> task's vruntime but it will be added again when the task returns to the
> fair class. The task's vruntime will have been erroneously doubled and
> the effective priority of the task will be reduced.
>
> Note this will also lead to inflation of all vruntimes since the doubled
> vruntime value will become the rq's min_vruntime when other tasks leave
> the rq. This leads to repeated doubling of the vruntime and priority
> penalty.
>
> Fix this by recognizing a WAKING task's vruntime as normalized only if
> sched_remote_wakeup is true. This indicates a migration, in which case
> the vruntime would have been normalized in migrate_task_rq_fair().
>
> Based on a similar patch from joaodias@google.com.
>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Steve Muckle <smuckle@google.com>
> ---
> kernel/sched/fair.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index b39fb596f6c1..b3b62cf37fb6 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9638,7 +9638,8 @@ static inline bool vruntime_normalized(struct task_struct *p)
> * - A task which has been woken up by try_to_wake_up() and
> * waiting for actually being woken up by sched_ttwu_pending().
> */
> - if (!se->sum_exec_runtime || p->state == TASK_WAKING)
> + if (!se->sum_exec_runtime ||
> + (p->state == TASK_WAKING && p->sched_remote_wakeup))
> return true;
>
> return false;
>

Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

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