linux-kernel - Re: [PATCH] task_work: simplify the task_work

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Date:   Tue, 15 Mar 2022 15:58:49 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Christoph Hellwig <hch@....de>, axboe@...nel.dk
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] task_work: simplify the task_work_add() interface

On Wed, Feb 23 2022 at 08:27, Christoph Hellwig wrote:
> Provide a low-level task_work_add_nonotify interface that just adds
> the work to the list and open code the TWA_SIGNAL and TWA_NONE callers
> using it.  task_work_add() itself now only handles the common TWA_RESUME
> case and can drop the notify argument.

There is a distinct lack of justification in that change log.

>  	worker->create_index = acct->index;
> -	if (!task_work_add(wq->task, &worker->create_work, TWA_SIGNAL)) {
> +	if (!task_work_add_nonotify(wq->task, &worker->create_work)) {
> +		set_notify_signal(wq->task);

I fail to see the improvement here.

> @@ -9606,7 +9606,7 @@ static __cold void io_ring_exit_work(struct work_struct *work)
>  					ctx_node);
>  		/* don't spin on a single task if cancellation failed */
>  		list_rotate_left(&ctx->tctx_list);
> -		ret = task_work_add(node->task, &exit.task_work, TWA_SIGNAL);
> +		ret = task_work_add_nonotify(node->task, &exit.task_work);

While I clearly see the regression in this case ...

>  		if (WARN_ON_ONCE(ret))
>  			continue;
>  /**
> - * task_work_add - ask the @task to execute @work->func()
> + * task_work_add_nonotify - ask the @task to execute @work->func()
>   * @task: the task which should run the callback
>   * @work: the callback to run
>   * @notify: how to notify the targeted task

This parameter is removed below ...

Thanks,

        tglx