On Tue, Feb 09, 2021 at 11:09:27PM +0000, Luck, Tony wrote: > > +#define X86_BUG_NUMA_SHARES_LLC X86_BUG(25) /* CPU may > > enumerate an LLC shared by multiple NUMA nodes */ > > During internal review I wondered why this is a "BUG" rather than a "FEATURE" > bit. > > Apparently, the suggestion for "BUG" came from earlier community discussions. > > Historically it may have seemed reasonable to say that a cache cannot span > NUMA domains. But with more and more things moving off the motherboard > and into the socket, this doesn't seem too weird now.
If you look at the details this SNC LLC span doesn't behave quite right either. It really isn't a regular cache, but behaves a bit like a mash-up of the s390 book caches and a normal LLC. Did anybody play with adding the book domain to these SNC configurations? Can we detect SNC other than by this quirk?
