Re: [PATCH 2/2] I386 convert pae wmb to non smp

[Nick Piggin <nickpiggin@yahoo.com.au>]

Zachary Amsden wrote:

> Nick Piggin wrote:
>
>> wmb() means that it also orders IO memory. It is no difference for
>> i386, but smp_wmb() actually has the right semantics of the abstract
>> Linux memory model.
>
>
> The name is pretty confused.  smp_wmb seems to imply an SMP-only 
> barrier, whereas we want here a write barrier on regular memory.


That is just a compiler barrier (barrier()). A CPU should always be 
consistent with
itself so memory ordering doesn't really apply there (hence smp_ prefix, 
which also
are compiler barriers, of course).

>   Both smp_wmb and wmb() are identical in that they both reduce to 
> barrier today, but I confess not to know which one semantically is 
> correct.


Well you're only looking at i386. True it is i386 specific code, but 
sticking
to the Linux memory model is more clear and consistent I think.

>   Your call on this patch - it is unecessary, I thought it was more 
> semantically correct, but you probably know that better than me.  So, 
> drop part 2 of this patch?


Yes, and make part 1 use smp_wmb.

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