linux-kernel - Re: [PATCH v3 08/57] sched: Simplify wake_up_if

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Date:   Mon, 12 Jun 2023 11:02:28 -0700
From:   Boqun Feng <boqun.feng@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
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Subject: Re: [PATCH v3 08/57] sched: Simplify wake_up_if_idle()

On Mon, Jun 12, 2023 at 11:07:21AM +0200, Peter Zijlstra wrote:
> Use guards to reduce gotos and simplify control flow.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/sched/core.c  |   20 ++++++--------------
>  kernel/sched/sched.h |   15 +++++++++++++++
>  2 files changed, 21 insertions(+), 14 deletions(-)
> 
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3872,21 +3872,13 @@ static void __ttwu_queue_wakelist(struct
>  void wake_up_if_idle(int cpu)
>  {
>  	struct rq *rq = cpu_rq(cpu);
> -	struct rq_flags rf;
>  
> -	rcu_read_lock();
> -
> -	if (!is_idle_task(rcu_dereference(rq->curr)))
> -		goto out;
> -
> -	rq_lock_irqsave(rq, &rf);
> -	if (is_idle_task(rq->curr))
> -		resched_curr(rq);
> -	/* Else CPU is not idle, do nothing here: */
> -	rq_unlock_irqrestore(rq, &rf);
> -
> -out:
> -	rcu_read_unlock();
> +	guard(rcu)();
> +	if (is_idle_task(rcu_dereference(rq->curr))) {
> +		guard(rq_lock)(rq);

We assume that irq must be disabled when this function called?
Otherwise, I don't understand why this is not

	guard(rq_lock_irqsave)(rq);

?

Regards,
Boqun

> +		if (is_idle_task(rq->curr))
> +			resched_curr(rq);
> +	}
>  }
>  
>  bool cpus_share_cache(int this_cpu, int that_cpu)
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1678,6 +1678,21 @@ rq_unlock(struct rq *rq, struct rq_flags
>  	raw_spin_rq_unlock(rq);
>  }
>  
> +DEFINE_LOCK_GUARD_1(rq_lock, struct rq,
> +		    rq_lock(_T->lock, &_T->rf),
> +		    rq_unlock(_T->lock, &_T->rf),
> +		    struct rq_flags rf)
> +
> +DEFINE_LOCK_GUARD_1(rq_lock_irq, struct rq,
> +		    rq_lock_irq(_T->lock, &_T->rf),
> +		    rq_unlock_irq(_T->lock, &_T->rf),
> +		    struct rq_flags rf)
> +
> +DEFINE_LOCK_GUARD_1(rq_lock_irqsave, struct rq,
> +		    rq_lock_irqsave(_T->lock, &_T->rf),
> +		    rq_unlock_irqrestore(_T->lock, &_T->rf),
> +		    struct rq_flags rf)
> +
>  static inline struct rq *
>  this_rq_lock_irq(struct rq_flags *rf)
>  	__acquires(rq->lock)
> 
>