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SubjectRe: [PATCH v5 2/2] sched/rt: Trying to push current task when target disable migrating
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Steven Rostedt <rostedt@goodmis.org> writes:

> On Tue, 12 Jul 2022 09:31:25 +0800
> Schspa Shi <schspa@gmail.com> wrote:
>
>> When the task to push disable migration, retry to push the current
>> running task on this CPU away, instead doing nothing for this migrate
>> disabled task.
>>
>> Signed-off-by: Schspa Shi <schspa@gmail.com>
>> ---
>> kernel/sched/core.c | 6 +++++-
>> kernel/sched/rt.c | 6 ++++++
>> 2 files changed, 11 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index da0bf6fe9ecdc..0b1fefd97d874 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -2509,8 +2509,12 @@ int push_cpu_stop(void *arg)
>> if (p->sched_class->find_lock_rq)
>> lowest_rq = p->sched_class->find_lock_rq(p, rq);
>>
>> - if (!lowest_rq)
>> + if (!lowest_rq) {
>
> Probably should add a comment reminding us that the find_lock() function
> above could have released the rq lock and allow p to schedule and be
> preempted again, and that lowest_rq could be NULL because p now has the
> migrate_disable flag set and not because it could not find the lowest rq.
>

OK, it will be better.

Let me upload a v6 patch for that.

> -- Steve
>
>
>> + if (unlikely(is_migration_disabled(p)))
>> + p->migration_flags |= MDF_PUSH;
>> +
>> goto out_unlock;
>> + }
>>
>> // XXX validate p is still the highest prio task
>> if (task_rq(p) == rq) {
>> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
>> index 7c32ba51b6d85..877380e465b7a 100644
>> --- a/kernel/sched/rt.c
>> +++ b/kernel/sched/rt.c
>> @@ -2136,6 +2136,12 @@ static int push_rt_task(struct rq *rq, bool pull)
>> */
>> task = pick_next_pushable_task(rq);
>> if (task == next_task) {
>> + /*
>> + * If next task has now disabled migrating, see if we
>> + * can push the current task.
>> + */
>> + if (unlikely(is_migration_disabled(task)))
>> + goto retry;
>> /*
>> * The task hasn't migrated, and is still the next
>> * eligible task, but we failed to find a run-queue


--
BRs
Schspa Shi

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