On Fri, Jul 24, 2015 at 12:31:01PM +0100, Will Deacon wrote:
> Hi Paul,
>
> On Wed, Jul 15, 2015 at 02:12:21PM +0100, Paul E. McKenney wrote:
> > On Wed, Jul 15, 2015 at 11:51:35AM +0100, Will Deacon wrote:
> > > On Wed, Jul 15, 2015 at 02:38:20AM +0100, Paul E. McKenney wrote:
> > > > On Tue, Jul 14, 2015 at 12:31:44PM -0700, Paul E. McKenney wrote:
> > > > > On Tue, Jul 14, 2015 at 03:12:16PM +0100, Will Deacon wrote:
> > > > > > On Tue, Jul 14, 2015 at 03:00:14PM +0100, Paul E. McKenney wrote:
> > > > > > > On Tue, Jul 14, 2015 at 01:51:46PM +0100, Will Deacon wrote:
> > > > > > > > On Tue, Jul 14, 2015 at 01:45:40PM +0100, Paul E. McKenney
> > > > > > > > wrote:
> > > > > > > > > On Tue, Jul 14, 2015 at 11:04:29AM +0100, Will Deacon wrote:
> > > > > > > > > > Given that RCU is currently the only user of this barrier,
> > > > > > > > > > how would you
> > > > > > > > > > feel about making the barrier local to RCU and not part of
> > > > > > > > > > the general
> > > > > > > > > > memory-barrier API?
> > > > > > > > >
> > > > > > > > > In theory, no objection. Your thought is to leave the
> > > > > > > > > definitions where
> > > > > > > > > they are, mark them as being used only by RCU, and removing
> > > > > > > > > mention from
> > > > > > > > > memory-barriers.txt? Or did you have something else in mind?
> > > > > > > >
> > > > > > > > Actually, I was thinking of defining them in an RCU header file
> > > > > > > > with an
> > > > > > > > #ifdef CONFIG_POWERPC for the smb_mb() version. Then you could
> > > > > > > > have a big
> > > > > > > > comment describing the semantics, or put that in an RCU
> > > > > > > > Documentation file
> > > > > > > > instead of memory-barriers.txt.
> > > > > > > >
> > > > > > > > That *should* then mean we notice anybody else trying to use
> > > > > > > > the barrier,
> > > > > > > > because they'd need to send patches to either add something
> > > > > > > > equivalent
> > > > > > > > or move the definition out again.
> > > > > > >
> > > > > > > My concern with this approach is that someone putting together a
> > > > > > > new
> > > > > > > architecture might miss this. That said, this approach certainly
> > > > > > > would
> > > > > > > work for the current architectures.
> > > > > >
> > > > > > I don't think they're any more likely to miss it than with the
> > > > > > current
> > > > > > situation where the generic code defines the macro as a NOP unless
> > > > > > you
> > > > > > explicitly override it.
> > > > >
> > > > > Fair enough...
> > > >
> > > > Like this?
> > >
> > > Precisely! Thanks for cooking the patch -- this lays all my worries to
> > > rest, so:
> > >
> > > Acked-by: Will Deacon <[email protected]>
> >
> > Thank you!
>
> [...]
>
> > > > commit 695c05d4b9666c50b40a1c022678b5f6e2e3e771
> > > > 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]>
>
> Are you planning to queue this somewhere? I think it makes sense regardless
> of whether we change PowerPc or not and ideally it would be merged around
> the same time as my relaxed atomics series.
I have is in -rcu. By default, I will push it to the 4.4 merge window.
Please let me know if you need it sooner.
Thanx, Paul
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