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Subject: Re: [PATCH -v2 15/17] sched: Fix migrate_disable() vs rt/dl balancing
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     tglx@linutronix.de, mingo@kernel.org, linux-kernel@vger.kernel.org,
        bigeasy@linutronix.de, qais.yousef@arm.com, swood@redhat.com,
        valentin.schneider@arm.com, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, rostedt@goodmis.org,
        bsegall@google.com, mgorman@suse.de, bristot@redhat.com,
        vincent.donnefort@arm.com, tj@kernel.org
References: <20201005145717.346020688@infradead.org>
 <20201005150922.458081448@infradead.org>
 <54bebe28-1d6d-5f71-da57-deb2eee111d3@arm.com>
 <20201012112824.GU2628@hirez.programming.kicks-ass.net>
From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
Message-ID: <c50326d5-4039-44f1-51e9-4adc0d3c57ea@arm.com>
Date:   Mon, 12 Oct 2020 14:22:54 +0200
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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).