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

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Message-ID: <1404407389.2498.3.camel@buesod1.americas.hpqcorp.net>
Date:	Thu, 03 Jul 2014 10:09:49 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jason Low <jason.low2@...com>, torvalds@...ux-foundation.org,
	paulmck@...ux.vnet.ibm.com, mingo@...nel.org, Waiman.Long@...com,
	linux-kernel@...r.kernel.org, riel@...hat.com,
	akpm@...ux-foundation.org, hpa@...or.com, andi@...stfloor.org,
	James.Bottomley@...senpartnership.com, rostedt@...dmis.org,
	tim.c.chen@...ux.intel.com, aswin@...com, scott.norton@...com,
	chegu_vinod@...com
Subject: Re: [RFC] Cancellable MCS spinlock rework

On Thu, 2014-07-03 at 09:31 +0200, Peter Zijlstra wrote:
> On Wed, Jul 02, 2014 at 10:30:03AM -0700, Jason Low wrote:
> > Would potentially reducing the size of the rw semaphore structure by 32
> > bits (for all architectures using optimistic spinning) be a nice
> > benefit?
> 
> Possibly, although I had a look at the mutex structure and we didn't
> have a hole to place it in, unlike what you found with the rwsem.

Yeah, and currently struct rw_semaphore is the largest lock we have in
the kernel. Shaving off space is definitely welcome.

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