linux-kernel - Re: [PATCH] rtmutex: multiple candidate owners without unrelated boosting

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Message-ID: <alpine.LFD.2.00.1012150850380.12146@localhost6.localdomain6>
Date:	Wed, 15 Dec 2010 09:02:38 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Lai Jiangshan <laijs@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Young <hidave.darkstar@...il.com>,
	Darren Hart <dvhart@...ux.intel.com>,
	Namhyung Kim <namhyung@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] rtmutex: multiple candidate owners without unrelated
 boosting

On Tue, 14 Dec 2010, Steven Rostedt wrote:

> On Tue, 2010-12-14 at 17:04 +0800, Lai Jiangshan wrote:
> 
> OK, I was looking at this in a bit more detail (the coffee finally set
> in) and I was at first looking to nuke the cand_owner since it is
> redundant to cand_seq. But I think we can nuke the cand_seq instead and
> use the top_waiter as the decider.

So you just use cand_owner (the name sucks) to flag that the waiter
has been woken up either by the boost code or by an unlock. The waiter
clears that flag with waiter->lock->wait_lock held before calling
schedule().

Though I think we do need it at all. wakeup of an already running task
is almost a nop, so having one less state to worry about is good.

Thanks,

	tglx
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