Re: [PATCH 3/5] sched: add a few helpers to wake up tasks on the current cpu

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Jan 10, 2023 at 01:30:08PM -0800, Andrei Vagin wrote:

> diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
> index d57a5c1c1cd9..a1931a79c05a 100644
> --- a/kernel/sched/completion.c
> +++ b/kernel/sched/completion.c
> @@ -38,6 +38,18 @@ void complete(struct completion *x)
>  }
>  EXPORT_SYMBOL(complete);
>  
> +void complete_on_current_cpu(struct completion *x)
> +{
> +	unsigned long flags;
> +
> +	raw_spin_lock_irqsave(&x->wait.lock, flags);
> +
> +	if (x->done != UINT_MAX)
> +		x->done++;
> +	swake_up_locked_on_current_cpu(&x->wait);
> +	raw_spin_unlock_irqrestore(&x->wait.lock, flags);
> +}
> +
>  /**
>   * complete_all: - signals all threads waiting on this completion
>   * @x:  holds the state of this particular completion
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 6478e819eb99..c81866821139 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6874,7 +6874,7 @@ asmlinkage __visible void __sched preempt_schedule_irq(void)
>  int default_wake_function(wait_queue_entry_t *curr, unsigned mode, int wake_flags,
>  			  void *key)
>  {
> -	WARN_ON_ONCE(IS_ENABLED(CONFIG_SCHED_DEBUG) && wake_flags & ~WF_SYNC);
> +	WARN_ON_ONCE(IS_ENABLED(CONFIG_SCHED_DEBUG) && wake_flags & ~(WF_SYNC|WF_CURRENT_CPU));
>  	return try_to_wake_up(curr->private, mode, wake_flags);
>  }
>  EXPORT_SYMBOL(default_wake_function);
> diff --git a/kernel/sched/swait.c b/kernel/sched/swait.c
> index 76b9b796e695..9ebe23868942 100644
> --- a/kernel/sched/swait.c
> +++ b/kernel/sched/swait.c
> @@ -31,6 +31,17 @@ void swake_up_locked(struct swait_queue_head *q)
>  }
>  EXPORT_SYMBOL(swake_up_locked);
>  
> +void swake_up_locked_on_current_cpu(struct swait_queue_head *q)
> +{
> +	struct swait_queue *curr;
> +
> +	if (list_empty(&q->task_list))
> +		return;
> +
> +	curr = list_first_entry(&q->task_list, typeof(*curr), task_list);
> +	try_to_wake_up(curr->task, TASK_NORMAL, WF_CURRENT_CPU);
> +	list_del_init(&curr->task_list);
> +}
>  /*
>   * Wake up all waiters. This is an interface which is solely exposed for
>   * completions and not for general usage.
> diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
> index 133b74730738..47803a0b8d5d 100644
> --- a/kernel/sched/wait.c
> +++ b/kernel/sched/wait.c
> @@ -161,6 +161,11 @@ int __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
>  }
>  EXPORT_SYMBOL(__wake_up);
>  
> +void __wake_up_on_current_cpu(struct wait_queue_head *wq_head, unsigned int mode, void *key)
> +{
> +	__wake_up_common_lock(wq_head, mode, 1, WF_CURRENT_CPU, key);
> +}
> +
>  /*
>   * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
>   */

So I hate this patch, it adds a whole ton of duplication and litter for
no real reason afaict. For instance you could've just added an
wake_flags argument to swake_up_locked(), there's not *that* many users
-- unlike complete().

And for complete() instead of fully duplicating the function (always a
bad idea) you could've made complete_flags() and implemented complete()
using that, or something.

Anyway, let me go (finally) have a look at Chen's patch, since that
might render all this moot.