linux-kernel - Re: [PATCH RFC] sched: introduce add_wait_queue_exclusive

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Date:	Tue, 18 Mar 2014 16:47:24 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Peng Tao <bergwolf@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Oleg Drokin <oleg.drokin@...el.com>,
	Andreas Dilger <andreas.dilger@...el.com>
Subject: Re: [PATCH RFC] sched: introduce add_wait_queue_exclusive_head

On 03/18, Peter Zijlstra wrote:
>
> I think we can avoid the entire function if we add
> WQ_FLAG_LIFO and make prepare_to_wait_event() DTRT.

Agreed, this looks very natural.

prepare_to_wait_event(WQ_FLAG_LIFO) should probably skip all "flags == 0"
entries before list_add(). Given that it is supposed that the users won't
mix exclusive and !exclusive, perhaps the additional list_for_each() won't
hurt?

> Then we only need to teach ___wait() about this; and I suppose we could
> make .exclusive=-1 be the LIFO flag.

Or we can change ___wait_event()

	-	if (exclusive)							\
	-		__wait.flags = WQ_FLAG_EXCLUSIVE;			\
	-	else								\
	-		__wait.flags = 0;					\
	+	__wait.flags = exclusive;					\

and obviously change the callers. Perhaps this argument should be renamed
then.

But I am fine either way, just I like the idea to extend the current
interface.

Oleg.

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