linux-kernel - Re: [RFC] Cancellable MCS spinlock rework

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Date:	Thu, 3 Jul 2014 08:31:22 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jason Low <jason.low2@...com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Waiman Long <Waiman.Long@...com>,
	Davidlohr Bueso <davidlohr@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Anvin <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	Jej B <James.Bottomley@...senpartnership.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>,
	"Vinod, Chegu" <chegu_vinod@...com>
Subject: Re: [RFC] Cancellable MCS spinlock rework

On Wed, Jul 2, 2014 at 9:39 PM, Jason Low <jason.low2@...com> wrote:
>
> And due to padding, the additional modification below reduces the
> size of struct rw_semaphore by 64 bits on my machine  :)

Well, I think you could also make 'count' just be 'int' instead of 'long'.

I don't think we'll support 2 _billion_ processes/threads waiting on
the same semaphore any time soon, so the 'long' seems a bit of an
overkill on 64-bit architectures.

          Linus.
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