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

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Message-ID: <20151026132601.GV2508@worktop.programming.kicks-ass.net>
Date:	Mon, 26 Oct 2015 14:26:01 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Daniel Wagner <daniel.wagner@...-carit.de>
Cc:	Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.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

On Mon, Oct 26, 2015 at 01:59:44PM +0100, Daniel Wagner wrote:
> 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.

Yes, that is equivalent, just more code. As I wrote in my last email; I
was lazy :-)
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