linux-kernel - Re: [PATCH v5 2/2] sched/rt: Trying to push current task when target disable migrating

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Date:   Tue, 12 Jul 2022 22:34:40 +0800
From:   Schspa Shi <schspa@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/2] sched/rt: Trying to push current task when
 target disable migrating


Steven Rostedt <rostedt@...dmis.org> writes:

> On Tue, 12 Jul 2022 09:31:25 +0800
> Schspa Shi <schspa@...il.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@...il.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