Re: [PATCH -v2 15/17] sched: Fix migrate_disable() vs rt/dl balancing

[Dietmar Eggemann]

On 12/10/2020 13:28, Peter Zijlstra wrote:
> On Mon, Oct 12, 2020 at 11:56:09AM +0200, Dietmar Eggemann wrote:
>> On 05/10/2020 16:57, Peter Zijlstra wrote:
>>
>> [...]
>>
>>> --- a/kernel/sched/rt.c
>>> +++ b/kernel/sched/rt.c
>>> @@ -1859,7 +1859,7 @@ static struct task_struct *pick_next_pus
>>>   * running task can migrate over to a CPU that is running a task
>>>   * of lesser priority.
>>>   */
>>> -static int push_rt_task(struct rq *rq)
>>> +static int push_rt_task(struct rq *rq, bool pull)
>>>  {
>>>  	struct task_struct *next_task;
>>>  	struct rq *lowest_rq;
>>> @@ -1873,6 +1873,34 @@ static int push_rt_task(struct rq *rq)
>>>  		return 0;
>>>  
>>>  retry:
>>> +	if (is_migration_disabled(next_task)) {
>>> +		struct task_struct *push_task = NULL;
>>> +		int cpu;
>>> +
>>> +		if (!pull || rq->push_busy)
>>> +			return 0;
>>
>> Shouldn't there be the same functionality in push_dl_task(), i.e.
>> returning 0 earlier for a task with migration_disabled?
> 
> No, deadline didn't implement HAVE_RT_PUSH_IPI. 

Right, so 'is_migration_disabled(next_task) && !pull' should never
happen then (for RT and DL).