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