On 07/17/2014 11:19 AM, Christoph Lameter wrote:
> Regarding atomic_t in per cpu areas: I am uncomfortable especially
> because both locked and unlocked RMW write operations could be acting on
> values in the same cacheline. I am concerned that the unlocked operation
> could have an unpredictable result.
>
>
> f.e. the following per cpu data structure
>
> struct test {
> atomic_t a;
> int b;
> } onecacheline;
>
>
> Local cpu does
>
> this_cpu_inc(onecacheline.b);
>
> If this is racing with a remote cpus:
>
> atomic_inc(percpu(&a, cpu))
>
> then we have on x86 a increment operation with locked semantics racing
> with an unlocked one on the same cacheline.
>
OK, I will add this as a warning in the documentation. Thanks!
--
Pranith
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