On Sun, Jan 15, 2017 at 08:57:11AM +0100, Ingo Molnar wrote:
>
> * Paul E. McKenney <[email protected]> wrote:
>
> > On Sun, Jan 15, 2017 at 08:11:23AM +0100, Ingo Molnar wrote:
> > >
> > > * Paul E. McKenney <[email protected]> wrote:
> > >
> > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > > > index 357b32aaea48..5fdfe874229e 100644
> > > > --- a/include/linux/rcupdate.h
> > > > +++ b/include/linux/rcupdate.h
> > > > @@ -1175,11 +1175,11 @@ do { \
> > > > * if the UNLOCK and LOCK are executed by the same CPU or if the
> > > > * UNLOCK and LOCK operate on the same lock variable.
> > > > */
> > > > -#ifdef CONFIG_PPC
> > > > +#ifdef CONFIG_ARCH_WEAK_RELACQ
> > > > #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for
> > > > lock. */
> > > > -#else /* #ifdef CONFIG_PPC */
> > > > +#else /* #ifdef CONFIG_ARCH_WEAK_RELACQ */
> > > > #define smp_mb__after_unlock_lock() do { } while (0)
> > > > -#endif /* #else #ifdef CONFIG_PPC */
> > > > +#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELACQ */
> > > >
> > > >
> > >
> > > So at the risk of sounding totally pedantic, why not structure it like
> > > the
> > > existing smp_mb__before/after*() primitives in barrier.h?
> > >
> > > That allows asm-generic/barrier.h to pick up the definition - for example
> > > in the
> > > case of smp_acquire__after_ctrl_dep() we do:
> > >
> > > #ifndef smp_acquire__after_ctrl_dep
> > > #define smp_acquire__after_ctrl_dep() smp_rmb()
> > > #endif
> > >
> > > Which allows Tile to relax it:
> > >
> > > arch/tile/include/asm/barrier.h:#define smp_acquire__after_ctrl_dep()
> > > barrier()
> > >
> > > I.e. I'd move the API definition out of rcupdate.h and into barrier.h -
> > > even
> > > though tree-RCU is the only user of this barrier type.
> >
> > I wouldn't have any problem with that, however, some time back it was
> > moved into RCU because (you guessed it!) RCU is the only user. ;-)
>
> Indeed ...
>
> [sounds of rummaging around in the Git tree]
>
> I found this commit of yours from ancient history (more than a year ago!):
>
> commit 12d560f4ea87030667438a169912380be00cea4b
> Author: Paul E. McKenney <[email protected]>
> Date: Tue Jul 14 18:35:23 2015 -0700
>
> rcu,locking: Privatize smp_mb__after_unlock_lock()
>
> RCU is the only thing that uses smp_mb__after_unlock_lock(), and is
> likely the only thing that ever will use it, so this commit makes this
> macro private to RCU.
>
> Signed-off-by: Paul E. McKenney <[email protected]>
> Cc: Will Deacon <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Benjamin Herrenschmidt <[email protected]>
> Cc: "[email protected]" <[email protected]>
>
> So I concur and I'm fine with your patch - or with the status quo code as
> well.
I already have the patch queued, so how about I keep it if I get an ack
from the powerpc guys and drop it otherwise?
Thanx, Paul
