Sorry for being tardy, I had a wee spell of feeling horrible and then I
procrastinated longer than I should have.
On Fri, Sep 11, 2015 at 01:45:07PM +0100, Will Deacon wrote:
> Peter, any thoughts? I'm not au fait with the x86 memory model, but what
> Paul's saying is worrying.
Right, so Paul is right -- and I completely forgot (I used to know about
that).
So all the TSO archs (SPARC-TSO, x86 (!OOSTORE) and s390) can do
smp_load_acquire()/smp_store_release() with just barrier(), and while:
smp_store_release(&x);
smp_load_acquire(&x);
will provide full order by means of the address dependency,
smp_store_release(&x);
smp_load_acquire(&y);
will not. Because the one reorder TSO allows is exactly that one.
> Peter -- if the above reordering can happen on x86, then moving away
> from RCpc is going to be less popular than I hoped...
Sadly yes.. We could of course try and split LOCK from ACQUIRE again,
but I'm not sure that's going to help anything except confusion.
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