Re: [PATCH v10 6/7] sched: Split out __schedule() deactivate task logic into a helper

[Metin Kaya <metin.kaya@arm.com>]

On 04/06/2024 2:29 pm, Qais Yousef wrote:
> On 05/06/24 21:54, John Stultz wrote:
>> As we're going to re-use the deactivation logic,
>> split it into a helper.
>>
>> Cc: Joel Fernandes <joelaf@google.com>
>> Cc: Qais Yousef <qyousef@layalina.io>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Juri Lelli <juri.lelli@redhat.com>
>> Cc: Vincent Guittot <vincent.guittot@linaro.org>
>> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
>> Cc: Valentin Schneider <vschneid@redhat.com>
>> Cc: Steven Rostedt <rostedt@goodmis.org>
>> Cc: Ben Segall <bsegall@google.com>
>> Cc: Zimuzo Ezeozue <zezeozue@google.com>
>> Cc: Youssef Esmat <youssefesmat@google.com>
>> Cc: Mel Gorman <mgorman@suse.de>
>> Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: Waiman Long <longman@redhat.com>
>> Cc: Boqun Feng <boqun.feng@gmail.com>
>> Cc: "Paul E. McKenney" <paulmck@kernel.org>
>> Cc: Metin Kaya <Metin.Kaya@arm.com>
>> Cc: Xuewen Yan <xuewen.yan94@gmail.com>
>> Cc: K Prateek Nayak <kprateek.nayak@amd.com>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: kernel-team@android.com
>> Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
>> Tested-by: Metin Kaya <metin.kaya@arm.com>
>> Reviewed-by: Metin Kaya <metin.kaya@arm.com>
>> Signed-off-by: John Stultz <jstultz@google.com>
>> ---
>> v6:
>> * Define function as static to avoid "no previous prototype"
>>    warnings as Reported-by: kernel test robot <lkp@intel.com>
>> v7:
>> * Rename state task_state to be more clear, as suggested by
>>    Metin Kaya
>> ---
>>   kernel/sched/core.c | 72 +++++++++++++++++++++++++++------------------
>>   1 file changed, 43 insertions(+), 29 deletions(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 48f0d4b381d5..8bc5844ebab9 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -6572,6 +6572,48 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
>>   # define SM_MASK_PREEMPT	SM_PREEMPT
>>   #endif
>>   
>> +/*
>> + * Helper function for __schedule()
>> + *
>> + * If a task does not have signals pending, deactivate it and return true
>> + * Otherwise marks the task's __state as RUNNING and returns false
>> + */
>> +static bool try_to_deactivate_task(struct rq *rq, struct task_struct *p,
>> +				   unsigned long task_state)
>> +{
>> +	if (signal_pending_state(task_state, p)) {
>> +		WRITE_ONCE(p->__state, TASK_RUNNING);
> 
> We can avoid extra indention for the other (lengthy) leg if we return here?
> 
> The return value is ignored for now, I don't mind keeping it but better call it

I see the return value is unused even after the complete patch set. So, 
agreed with your proposal.

> out in the commit message or when you add the new user later you can update the
> signature more easily.
> 
> Generally I think patches 4, 5 and 6 could be sent as their own series with
> minor commit messages tweaks to make them more independent and I hope Ingo and
> Peter are okay to pick them up as they look a nice clean up in general.
> 
> Anyway:
> 
> Reviewed-by: Qais Yousef <qyousef@layalina.io>
> 
>> +	} else {
>> +		p->sched_contributes_to_load =
>> +			(task_state & TASK_UNINTERRUPTIBLE) &&
>> +			!(task_state & TASK_NOLOAD) &&
>> +			!(task_state & TASK_FROZEN);
>> +
>> +		if (p->sched_contributes_to_load)
>> +			rq->nr_uninterruptible++;
>> +
>> +		/*
>> +		 * __schedule()			ttwu()
>> +		 *   prev_state = prev->state;    if (p->on_rq && ...)
>> +		 *   if (prev_state)		    goto out;
>> +		 *     p->on_rq = 0;		  smp_acquire__after_ctrl_dep();
>> +		 *				  p->state = TASK_WAKING
>> +		 *
>> +		 * Where __schedule() and ttwu() have matching control dependencies.
>> +		 *
>> +		 * After this, schedule() must not care about p->state any more.
>> +		 */
>> +		deactivate_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_NOCLOCK);
>> +
>> +		if (p->in_iowait) {
>> +			atomic_inc(&rq->nr_iowait);
>> +			delayacct_blkio_start();
>> +		}
>> +		return true;
>> +	}
>> +	return false;
>> +}
>> +
>>   /*
>>    * __schedule() is the main scheduler function.
>>    *
>> @@ -6665,35 +6707,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
>>   	 */
>>   	prev_state = READ_ONCE(prev->__state);
>>   	if (!(sched_mode & SM_MASK_PREEMPT) && prev_state) {
>> -		if (signal_pending_state(prev_state, prev)) {
>> -			WRITE_ONCE(prev->__state, TASK_RUNNING);
>> -		} else {
>> -			prev->sched_contributes_to_load =
>> -				(prev_state & TASK_UNINTERRUPTIBLE) &&
>> -				!(prev_state & TASK_NOLOAD) &&
>> -				!(prev_state & TASK_FROZEN);
>> -
>> -			if (prev->sched_contributes_to_load)
>> -				rq->nr_uninterruptible++;
>> -
>> -			/*
>> -			 * __schedule()			ttwu()
>> -			 *   prev_state = prev->state;    if (p->on_rq && ...)
>> -			 *   if (prev_state)		    goto out;
>> -			 *     p->on_rq = 0;		  smp_acquire__after_ctrl_dep();
>> -			 *				  p->state = TASK_WAKING
>> -			 *
>> -			 * Where __schedule() and ttwu() have matching control dependencies.
>> -			 *
>> -			 * After this, schedule() must not care about p->state any more.
>> -			 */
>> -			deactivate_task(rq, prev, DEQUEUE_SLEEP | DEQUEUE_NOCLOCK);
>> -
>> -			if (prev->in_iowait) {
>> -				atomic_inc(&rq->nr_iowait);
>> -				delayacct_blkio_start();
>> -			}
>> -		}
>> +		try_to_deactivate_task(rq, prev, prev_state);
>>   		switch_count = &prev->nvcsw;
>>   	}
>>   
>> -- 
>> 2.45.0.rc1.225.g2a3ae87e7f-goog
>>