linux-kernel - Re: [PATCH v7 1/4] qrwlock: A queue read/write lock implementation

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Message-ID: <20131218185910.GS19211@linux.vnet.ibm.com>
Date:	Wed, 18 Dec 2013 10:59:10 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Waiman Long <waiman.long@...com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michel Lespinasse <walken@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Rik van Riel <riel@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	George Spelvin <linux@...izon.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>, aswin@...com,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH v7 1/4] qrwlock: A queue read/write lock implementation

On Wed, Dec 18, 2013 at 01:45:01PM -0500, Waiman Long wrote:
> On 12/17/2013 02:21 PM, Paul E. McKenney wrote:

[ . . . ]

> >>+	signal_next(lock,&node);
> >Good, this allows multiple readers to acquire the lock concurrently,
> >give or take memory latency compared to critical-section duration.
> >When the first writer shows up, it presumably spins on the lock word.
> >
> 
> Yes, that was the intention. The first writer that shows up will
> block succeeding readers from getting the lock.
> 
> BTW, what was the status of the TSO memory barrier patch? This patch
> has some partial dependency it.

I am hoping that it makes it into -tip soon, as I also have a patch that
depends on it.

							Thanx, Paul

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