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

[Christoph Lameter]

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.


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