linux-kernel - Re: [PATCH RFC tip/lkmm 08/10] EXP Remove understore from smp_mb__before

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Date:   Thu, 15 Feb 2018 15:32:59 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Andrea Parri <parri.andrea@...il.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        stern@...land.harvard.edu, will.deacon@....com,
        peterz@...radead.org, boqun.feng@...il.com, npiggin@...il.com,
        dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr,
        akiyks@...il.com
Subject: Re: [PATCH RFC tip/lkmm 08/10] EXP Remove understore from
 smp_mb__before_atomic() workings

On Fri, Feb 16, 2018 at 12:19:58AM +0100, Andrea Parri wrote:
> On Thu, Feb 15, 2018 at 02:49:37PM -0800, Paul E. McKenney wrote:
> > On Thu, Feb 15, 2018 at 11:30:09PM +0100, Andrea Parri wrote:
> > > On Fri, Feb 09, 2018 at 06:20:29AM -0800, Paul E. McKenney wrote:
> > > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > > 
> > > nit: s/understore/underscore  (a very understandable lapsus, BTW ;-)
> > 
> > ;-)
> > 
> > Will fix when squashing.
> > 
> > > According to the cover letter, patches 8-10 of this series are intended
> > > to be squashed together;  it could be useful to add a description then:
> > > the motivation for these changes might appear "trivial" today;  months/
> > > years from now?  mmh, I can't put my finger on it ;-)
> > 
> > Assuming we keep these patches, agreed.  Something like this for the
> > aggregated single commit, perhaps:
> > 
> > 	tools/memory-model: Convert underscores to hyphens
> > 
> > 	Typical cat-language code uses hyphens for word separators in
> > 	identifiers, but several LKMM identifiers use underscores instead.
> > 	This commit therefore converts the underscores in the .bell and
> > 	.cat files for smp_mb__before_atomic(), smp_mb__after_atomic(),
> > 	and smp_mb__after_spinlock() to hyphens.
> > 
> > > IMO,  this descrition should also mention why this solution "is the way
> > > to go" (e.g., compare with the solution recently implemented by Akira).
> > 
> > You lost me here.  Or are you asking for a commit log similar to that
> > provided by Akira for his forward-port of Alan's unrelated patch?  If
> > so, please see above.
> 
> I was mainly thinking "but rb_dep...";  or you're also planning to
> rename this annotation and, maybe, the "rb-dep" relation (in order
> to avoid the conflict)?

The rb_dep relation goes away completely once we catch LKMM up with
the recent changes that remove smp_read_barrier_depends() from the
core kernel.  So my current thought is hold back the "_"->"-" commit
until that catch-up happens.

							Thanx, Paul

>   Andrea
> 
> 
> > 
> > 							Thanx, Paul
> > 
> > >   Andrea
> > > 
> > > 
> > > > ---
> > > >  tools/memory-model/linux-kernel.bell | 2 +-
> > > >  tools/memory-model/linux-kernel.cat  | 2 +-
> > > >  tools/memory-model/linux-kernel.def  | 2 +-
> > > >  3 files changed, 3 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/tools/memory-model/linux-kernel.bell b/tools/memory-model/linux-kernel.bell
> > > > index b984bbda01a5..558bbef9e08a 100644
> > > > --- a/tools/memory-model/linux-kernel.bell
> > > > +++ b/tools/memory-model/linux-kernel.bell
> > > > @@ -28,7 +28,7 @@ enum Barriers = 'wmb (*smp_wmb*) ||
> > > >  		'rcu-lock (*rcu_read_lock*)  ||
> > > >  		'rcu-unlock (*rcu_read_unlock*) ||
> > > >  		'sync-rcu (*synchronize_rcu*) ||
> > > > -		'before_atomic (*smp_mb__before_atomic*) ||
> > > > +		'before-atomic (*smp_mb__before_atomic*) ||
> > > >  		'after_atomic (*smp_mb__after_atomic*) ||
> > > >  		'after_spinlock (*smp_mb__after_spinlock*)
> > > >  instructions F[Barriers]
> > > > diff --git a/tools/memory-model/linux-kernel.cat b/tools/memory-model/linux-kernel.cat
> > > > index babe2b3b0bb3..31c08a44c088 100644
> > > > --- a/tools/memory-model/linux-kernel.cat
> > > > +++ b/tools/memory-model/linux-kernel.cat
> > > > @@ -29,7 +29,7 @@ let rb-dep = [R] ; fencerel(Rb_dep) ; [R]
> > > >  let rmb = [R \ Noreturn] ; fencerel(Rmb) ; [R \ Noreturn]
> > > >  let wmb = [W] ; fencerel(Wmb) ; [W]
> > > >  let mb = ([M] ; fencerel(Mb) ; [M]) |
> > > > -	([M] ; fencerel(Before_atomic) ; [RMW] ; po? ; [M]) |
> > > > +	([M] ; fencerel(Before-atomic) ; [RMW] ; po? ; [M]) |
> > > >  	([M] ; po? ; [RMW] ; fencerel(After_atomic) ; [M]) |
> > > >  	([M] ; po? ; [LKW] ; fencerel(After_spinlock) ; [M])
> > > >  let gp = po ; [Sync-rcu] ; po?
> > > > diff --git a/tools/memory-model/linux-kernel.def b/tools/memory-model/linux-kernel.def
> > > > index a397387f77cc..ff4b756f4a44 100644
> > > > --- a/tools/memory-model/linux-kernel.def
> > > > +++ b/tools/memory-model/linux-kernel.def
> > > > @@ -21,7 +21,7 @@ smp_mb() { __fence{mb} ; }
> > > >  smp_rmb() { __fence{rmb} ; }
> > > >  smp_wmb() { __fence{wmb} ; }
> > > >  smp_read_barrier_depends() { __fence{rb_dep}; }
> > > > -smp_mb__before_atomic() { __fence{before_atomic} ; }
> > > > +smp_mb__before_atomic() { __fence{before-atomic} ; }
> > > >  smp_mb__after_atomic() { __fence{after_atomic} ; }
> > > >  smp_mb__after_spinlock() { __fence{after_spinlock} ; }
> > > >  
> > > > -- 
> > > > 2.5.2
> > > > 
> > > 
> > 
>