Re: [PATCH v3] x86,sched: allow topologies where NUMA nodes share an LLC

[Dave Hansen]

On 03/29/2018 06:47 AM, Peter Zijlstra wrote:
> Further I think Dave argued that we should not change the llc-size,
> because while SNC presents a subset of the cache to local CPUs, for
> remote data the whole cache is still available, again something some
> applications might rely on.

BTW, I may have argued this in the past, but I don't think it's the best
thing to do.

If anything, we should optimize for the _users_ of this information: the
performance-sensitive ones who are digging up the cache topology.  They
are also likely to be the most NUMA-affinitized and stay node-local with
much of their memory traffic.  That would seem to point us in the
direction of enumerating two separate, half-sized LLCs "shared" only by
the slice when SNC mode is on.

That's what I've argued to the hardware folks lately, at least.