linux-kernel - Re: [PATCH v3 1/4] wait.[ch]: Introduce the simple waitqueue (swait) implementation

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Message-ID: <562E23C0.9000500@bmw-carit.de>
Date:	Mon, 26 Oct 2015 13:59:44 +0100
From:	Daniel Wagner <daniel.wagner@...-carit.de>
To:	Boqun Feng <boqun.feng@...il.com>
CC:	<linux-kernel@...r.kernel.org>, <linux-rt-users@...r.kernel.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 1/4] wait.[ch]: Introduce the simple waitqueue (swait)
 implementation

Hi Boqun,

On 10/26/2015 01:04 PM, Boqun Feng wrote:
> On Tue, Oct 20, 2015 at 09:28:07AM +0200, Daniel Wagner wrote:
>> +
>> +/*
>> + * The thing about the wake_up_state() return value; I think we can ignore it.
>> + *
>> + * If for some reason it would return 0, that means the previously waiting
>> + * task is already running, so it will observe condition true (or has already).
>> + */
>> +void swake_up_locked(struct swait_queue_head *q)
>> +{
>> +	struct swait_queue *curr;
>> +
>> +	list_for_each_entry(curr, &q->task_list, task_list) {
>> +		wake_up_process(curr->task);
>> +		list_del_init(&curr->task_list);
>> +		break;
> 
> Just be curious, what's this break for? Or what's this loop(?) for?

I have to guess here, since Peter wrote it. It looks like the function
is based on __wake_up_common(). Though I agree the loop is not necessary
and something like below should the trick. Unless I do not see something
important.

	void swake_up_locked(struct swait_queue_head *q)
	{
		struct swait_queue *curr;

		if (list_emtpy(&q))
			return;

		curr = list_first_entry(&q, typeof(*curr), task_list);
		wake_up_process(curr->task);
		list_del_init(&curr->task_list);
	}

If Peter is not complaining I change swake_up_locked() for the next version.

Thanks,
Daniel
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