Message-ID: <1404412485.8764.33.camel@j-VirtualBox>
Subject: Re: [RFC] Cancellable MCS spinlock rework
From: Jason Low <jason.low2@hp.com>
To: Davidlohr Bueso <davidlohr@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>, 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
Date: Thu, 03 Jul 2014 11:34:45 -0700
In-Reply-To: <1404407389.2498.3.camel@buesod1.americas.hpqcorp.net>
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On Thu, 2014-07-03 at 10:09 -0700, Davidlohr Bueso wrote:
> 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.

Right, especially if it could help things like xfs inode.

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