linux-kernel - Re: [PATCH 1/2] sched/wait: add round robin wakeup mode

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Message-ID: <20150210161154.GY21418@twins.programming.kicks-ass.net>
Date:	Tue, 10 Feb 2015 17:11:54 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jason Baron <jbaron@...mai.com>
Cc:	mingo@...hat.com, viro@...iv.linux.org.uk,
	akpm@...ux-foundation.org, normalperson@...t.net,
	davidel@...ilserver.org, mtk.manpages@...il.com,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/2] sched/wait: add round robin wakeup mode

On Tue, Feb 10, 2015 at 10:59:01AM -0500, Jason Baron wrote:
> hmmm...but don't we need the head/tail of the list to add it back too?

Ah, good point that ;-)

> Further, we can't just append to tail while walking the list b/c
> otherwise it can result in multiple wakeups to the same item. So I could
> add to a local list, for example, in __wake_up_common(). And then just
> add that to the tail once the list_for_each() finishes.

True; you can do horrible things, but I think that is the safest option
indeed.

> In terms of the flag, maybe another option would be to have the
> wait_queue_func_t return a 'ROTATE_ME' value instead
> of 1, since I think we currently only make use of 0 and 1?

Lets stick with the flag then.
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