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Date: Tue, 4 Jun 2024 14:55:36 +0100
From: Metin Kaya <metin.kaya@....com>
To: Qais Yousef <qyousef@...alina.io>, John Stultz <jstultz@...gle.com>
Cc: LKML <linux-kernel@...r.kernel.org>, Joel Fernandes <joelaf@...gle.com>,
Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Valentin Schneider <vschneid@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
Zimuzo Ezeozue <zezeozue@...gle.com>, Youssef Esmat
<youssefesmat@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>,
Boqun Feng <boqun.feng@...il.com>, "Paul E. McKenney" <paulmck@...nel.org>,
Xuewen Yan <xuewen.yan94@...il.com>, K Prateek Nayak
<kprateek.nayak@....com>, Thomas Gleixner <tglx@...utronix.de>,
kernel-team@...roid.com
Subject: Re: [PATCH v10 6/7] sched: Split out __schedule() deactivate task
logic into a helper
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@...gle.com>
>> Cc: Qais Yousef <qyousef@...alina.io>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Juri Lelli <juri.lelli@...hat.com>
>> Cc: Vincent Guittot <vincent.guittot@...aro.org>
>> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
>> Cc: Valentin Schneider <vschneid@...hat.com>
>> Cc: Steven Rostedt <rostedt@...dmis.org>
>> Cc: Ben Segall <bsegall@...gle.com>
>> Cc: Zimuzo Ezeozue <zezeozue@...gle.com>
>> Cc: Youssef Esmat <youssefesmat@...gle.com>
>> Cc: Mel Gorman <mgorman@...e.de>
>> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
>> Cc: Will Deacon <will@...nel.org>
>> Cc: Waiman Long <longman@...hat.com>
>> Cc: Boqun Feng <boqun.feng@...il.com>
>> Cc: "Paul E. McKenney" <paulmck@...nel.org>
>> Cc: Metin Kaya <Metin.Kaya@....com>
>> Cc: Xuewen Yan <xuewen.yan94@...il.com>
>> Cc: K Prateek Nayak <kprateek.nayak@....com>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: kernel-team@...roid.com
>> Tested-by: K Prateek Nayak <kprateek.nayak@....com>
>> Tested-by: Metin Kaya <metin.kaya@....com>
>> Reviewed-by: Metin Kaya <metin.kaya@....com>
>> Signed-off-by: John Stultz <jstultz@...gle.com>
>> ---
>> v6:
>> * Define function as static to avoid "no previous prototype"
>> warnings as Reported-by: kernel test robot <lkp@...el.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@...alina.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
>>
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