[PATCH 2/2] arm64: bpf: add BPF XADD instruction

[Peter Zijlstra]

On Wed, Nov 11, 2015 at 07:31:28PM +0100, Peter Zijlstra wrote:
> > Adding new intrinsic to llvm is not a big deal. I'll add it as soon
> > as I have time to work on it or if somebody beats me to it I would be
> > glad to test it and apply it.
> 
> This isn't a speed coding contest. You want to think about this
> properly.

That is, I don't think you want to go add LLVM intrinsics at all. You
want to piggy back on the memory model work done by the C/C++11 people.

What you want to think about is what the memory model of your virtual
machine is and how many instructions you want to expose for that.

Concurrency is a right pain, a little time and effort now will safe
heaps of pain down the road.