linux-kernel - Re: [PATCH v3 3/5] MCS Lock: Barrier corrections

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Date:	Thu, 07 Nov 2013 17:16:32 -0800
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Waiman Long <waiman.long@...com>,
	Arnd Bergmann <arnd@...db.de>, Rik van Riel <riel@...hat.com>,
	Aswin Chandramouleeswaran <aswin@...com>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	"Figo. zhang" <figo1802@...il.com>, linux-arch@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>,
	George Spelvin <linux@...izon.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Hurley <peter@...leysoftware.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Alex Shi <alex.shi@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Scott J Norton <scott.norton@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dave Hansen <dave.hansen@...el.com>,
	Matthew R Wilcox <matthew.r.wilcox@...el.com>,
	Will Deacon <will.deacon@....com>,
	Davidlohr Bueso <davidlohr.bueso@...com>
Subject: Re: [PATCH v3 3/5] MCS Lock: Barrier corrections

On Thu, 2013-11-07 at 14:43 -0800, Michel Lespinasse wrote:
> On Thu, Nov 7, 2013 at 2:21 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Thu, Nov 07, 2013 at 01:15:51PM -0800, Tim Chen wrote:
> >> Michel, are you planning to do an implementation of
> >> load-acquire/store-release functions of various architectures?
> >
> > A little something like this:
> > http://marc.info/?l=linux-arch&m=138386254111507
> >
> > It so happens we were working on that the past week or so due to another
> > issue ;-)
> 
> Haha, awesome, I wasn't aware of this effort.
> 
> Tim: my approach would be to provide the acquire/release operations in
> arch-specific include files, and have a default implementation using
> barriers for arches who don't provide these new ops. That way you make
> it work on all arches at once (using the default implementation) and
> make it fast on any arch that cares.
> 
> >> Or is the approach of arch specific memory barrier for MCS
> >> an acceptable one before load-acquire and store-release
> >> are available?  Are there any technical issues remaining with
> >> the patchset after including including Waiman's arch specific barrier?
> 
> I don't want to stand in the way of Waiman's change, and I had
> actually taken the same approach with arch-specific barriers when
> proposing some queue spinlocks in the past; however I do feel that
> this comes back regularly enough that having acquire/release
> primitives available would help, hence my proposal.
> 
> That said, earlier in the thread Linus said we should probably get all
> our ducks in a row before going forward with this, so...
> 

With the load_acquire and store_release implemented, it should be
pretty straightforward to implement MCS with them.  I'll respin
the patch series with these primitives.

Thanks.

Tim

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