From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH v6 0/5] MCS Lock: MCS lock code cleanup and optimizations Date: Wed, 20 Nov 2013 09:16:18 -0800 Message-ID: <20131120171618.GK4138@linux.vnet.ibm.com> References: <1384911446.11046.450.camel@schen9-DESK> <20131120101957.GA19352@mudshark.cambridge.arm.com> <1384966847.11046.457.camel@schen9-DESK> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1384966847.11046.457.camel@schen9-DESK> Sender: owner-linux-mm@kvack.org To: Tim Chen Cc: Will Deacon , Ingo Molnar , Andrew Morton , Thomas Gleixner , "linux-kernel@vger.kernel.org" , linux-mm , "linux-arch@vger.kernel.org" , Linus Torvalds , Waiman Long , Andrea Arcangeli , Alex Shi , Andi Kleen , Michel Lespinasse , Davidlohr Bueso , Matthew R Wilcox , Dave Hansen , Peter Zijlstra , Rik van Riel , Peter Hurley List-Id: linux-arch.vger.kernel.org On Wed, Nov 20, 2013 at 09:00:47AM -0800, Tim Chen wrote: > On Wed, 2013-11-20 at 10:19 +0000, Will Deacon wrote: > > Hi Tim, > > > > On Wed, Nov 20, 2013 at 01:37:26AM +0000, Tim Chen wrote: > > > In this patch series, we separated out the MCS lock code which was > > > previously embedded in the mutex.c. This allows for easier reuse of > > > MCS lock in other places like rwsem and qrwlock. We also did some micro > > > optimizations and barrier cleanup. > > > > > > The original code has potential leaks between critical sections, which > > > was not a problem when MCS was embedded within the mutex but needs > > > to be corrected when allowing the MCS lock to be used by itself for > > > other locking purposes. > > > > > > Proper barriers are now embedded with the usage of smp_load_acquire() in > > > mcs_spin_lock() and smp_store_release() in mcs_spin_unlock. See > > > http://marc.info/?l=linux-arch&m=138386254111507 for info on the > > > new smp_load_acquire() and smp_store_release() functions. > > > > > > This patches were previously part of the rwsem optimization patch series > > > but now we spearate them out. > > > > > > We have also added hooks to allow for architecture specific > > > implementation of the mcs_spin_lock and mcs_spin_unlock functions. > > > > > > Will, do you want to take a crack at adding implementation for ARM > > > with wfe instruction? > > > > Sure, I'll have a go this week. Thanks for keeping that as a consideration! > > > > As an aside: what are you using to test this code, so that I can make sure I > > don't break it? > > I was testing it against my rwsem patches. But any workload that > exercises mutex should also use this code, as this is part of mutex. It would be good to have more focused tests. It is amazing how reliable broken synchronization-primitive implementations can be. Of course, in this case, they will fail at the least opportune and most difficult to debug situation... Thanx, Paul -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org