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

[Tejun Heo]

On Tue, Jun 17, 2014 at 02:39:46PM -0500, Christoph Lameter wrote:
> On Tue, 17 Jun 2014, Paul E. McKenney wrote:
> 
> > 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.
> 
> Well that only occurs on initialization before the address of the
> struct that contains the offset is available to other processors.

So does assignment of the pointer in most cases.

> During operation the percpu area functions like a single processor. And
> its designed that way to avoid synchronization issues and take full
> advantage of *no* synchronization for full speed. We compromise on that
> for statistics but that is only read access.

And during normal operation, it doesn't make any difference for
anything except alpha.  It's about making the initialization part
easier / safer.

Thanks.

-- 
tejun
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