linux-kernel - Re: [PATCH v8 3/6] MCS Lock: optimizations and extra comments

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Message-ID: <20140121101742.GR31570@twins.programming.kicks-ass.net>
Date:	Tue, 21 Jan 2014 11:17:42 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E.McKenney" <paulmck@...ux.vnet.ibm.com>,
	Will Deacon <will.deacon@....com>,
	linux-kernel@...r.kernel.org, linux-mm <linux-mm@...ck.org>,
	linux-arch@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Waiman Long <waiman.long@...com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Alex Shi <alex.shi@...aro.org>,
	Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Matthew R Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	George Spelvin <linux@...izon.com>,
	"H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
	Aswin Chandramouleeswaran <aswin@...com>,
	Scott J Norton <scott.norton@...com>,
	"Figo.zhang" <figo1802@...il.com>
Subject: Re: [PATCH v8 3/6] MCS Lock: optimizations and extra comments

On Mon, Jan 20, 2014 at 05:24:28PM -0800, Tim Chen wrote:
> @@ -41,8 +47,11 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
>  
>  	prev = xchg(lock, node);
>  	if (likely(prev == NULL)) {
> -		/* Lock acquired */
> -		node->locked = 1;
> +		/* Lock acquired, don't need to set node->locked to 1
> +		 * as lock owner and other contenders won't check this value.
> +		 * If a debug mode is needed to audit lock status, then
> +		 * set node->locked value here.
> +		 */

Fail in comment style.

>  		return;
>  	}
>  	ACCESS_ONCE(prev->next) = node;
--
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