Re: [thiscpuops upgrade 10/10] Lockless (and preemptless) fastpathsfor slub

[Jeremy Fitzhardinge]

On 11/24/2010 08:17 AM, Christoph Lameter wrote:
> On Wed, 24 Nov 2010, Pekka Enberg wrote:
>
>>> +       /*
>>> +        * The transaction ids are globally unique per cpu and per operation on
>>> +        * a per cpu queue. Thus they can be guarantee that the cmpxchg_double
>>> +        * occurs on the right processor and that there was no operation on the
>>> +        * linked list in between.
>>> +        */
>>> +       tid = c->tid;
>>> +       barrier();
>> You're using a compiler barrier after every load from c->tid. Why?
> To make sure that the compiler does not do something like loading the tid
> later. The tid must be obtained before the rest of the information from
> the per cpu slab data is retrieved in order to ensure that we have a
> consistent set of data to operate on.

Isn't that best expressed with ACCESS_ONCE()?

    J
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