Re: [PATCH RFC] percpu: add data dependency barrier in percpu accessors and operations

[Paul E. McKenney]

On Tue, Jun 17, 2014 at 01:47:01PM -0500, Christoph Lameter wrote:
> 
> On Tue, 17 Jun 2014, Linus Torvalds wrote:
> 
> > On Jun 17, 2014 6:28 AM, "Christoph Lameter" <cl@xxxxxxxxxx> wrote:
> > >
> > > Even alpha maintains the illusion of changes becoming visible in the
> > > proper order for the currently executing thread. No barriers are needed.
> >
> > No Christoph, alpha really doesn't. Barriers needed.
> 
> Everythig breaks if a single hardware execution thread can no longer
> observe a consistent view of the world of the data it modifies.
> 
> We are not talking about synchronization here between multiple hardware
> threads. This is simply code running on a single hardware thread and all
> architectures maintain the uniprocessor illusion there.

We are talking about one CPU initializing all CPUs' portions of
dynamically allocated per-CPU memory, so there really is more than
one CPU involved.

							Thanx, Paul

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/