Re: [PATCH v6 0/5] MCS Lock: MCS lock code cleanup and optimizations

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On Wed, Nov 20, 2013 at 10:19:57AM +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?

+1 to that!  In fact, it would be nice to have the test code in-tree,
especially if it can test a wide variety of locks.  (/me needs to look
at what test code for locks might already be in tree, for that matter...)

							Thanx, Paul

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