Re: [PATCH v4 0/4] Add lightweight memory barriers for coherent memory access

From: Linus Torvalds
Date: Tue Nov 18 2014 - 15:53:40 EST

On Tue, Nov 18, 2014 at 9:28 AM, Alexander Duyck
<alexander.h.duyck@xxxxxxxxxx> wrote:
> These patches introduce two new primitives for synchronizing cache coherent
> memory writes and reads. These two new primitives are:
> coherent_rmb()
> coherent_wmb()

So I'm still not convinced about the name. I don't hate it, but if you
ever want to do "read_acquire", then that whole "coherent_" thing does
make for a big mouthful. I don't see why "dma" isn't simpler and more
to the point, and has the advantage of lining up (in documentation
etc) with "smp".

Why would you ever use "coherent_xyz()" on something that isn't about
dma? If it's cache-coherent memory without DMA, you'd use "smp_xyz()",
so I really do prefer that whole "dma-vs-smp" issue, because it talks
about what is actually the important issue. All sane memory is
coherent, after all (and if it isn't, you have other issues than
memory ordering).

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