On Wed, Feb 20, 2019 at 10:08:48AM -0500, Len Brown wrote: > Thanks for the comments, Peter. I'll update the patch to address the > syntax points. (Maybe checkpatch.pl should be updated to reflect your > preferences?). Don't know about checkpatch; I ignore plenty of its output. I think tglx started a document somewhere for what tip prefers, but I'm not sure where that went. > About macros vs C. I agree with your preference. > I used macros to be consistent with the existing code, and to be as > backport friendly as possible. > (a number of distros need to pull these patches into their supported kernels) > Sure, I'm willing to write in a cosmetic-only patch, after the > functional changes are upstream. Fair enough. > > It would've been nice to have the CPUID instruction 1F leaf reference > > 3B-3.9 in the SDM, and maybe mention this here too. > > I didn't mention SDM sections because they change -- leaving stale > pointers in our commit messages. The SDM is re-published 4 times per > year. Yah, I know. Which is why I keep all SDMs. So if you say, book 3 section 8 of Jul'17, I can find it :-) > > You haven't explained, and I can't readily find it in the SDM either, > > how these topology bits relate to caches and interconnects. > > > > Will these die thingies share LLC, or will LLC be per die. Will NUMA > > span dies or not. > > Excellent question. > Cache enumeration in Leaf-4 is totally unchanged. > ACPI NUMA tables are totally unchanged. Sure; and yet Sub-NUMA-Clustering broke stuff in interesting ways. I'm trying to get a feel for how these levels will interact with all that. Before that SNC stuff, caches had never spanned NODEs (and I still think that is 'creative' at best). > From a scheduler point of view, imagine that a SKX system with 4 die > in 4 packages was mechanically re-designed so that those 4 die resided > in 2 double-sized packages. > > They may have tweaked the links between the die, but logically it is > identical and compatible, and the legacy kernel will function > properly. This example has LLC in die and yes that works. But I can imagine things like L2 in tile and L3 across tiles but within DIE and then it _might_ make sense to still consider the tile for scheduling. Another option is having the LLC off die; also not unheard of. And then there's many creative and slightly crazy ways this can all be combined :/ > So the effect of Leaf B,1F is that it defines the scope of MSRs. eg. > what processors does a die-scope MSR cover. That is why the rest of > the patch is about sysfs topology, and about package MSR scope. > > Yes, there will be more exotic MSR situations in future products -- > the first ones are pretty simple -- something called a > package-scope-MSR in the SDM today becomes a die-scope-MSR in this > generation on a multi-die/package system. Yes :-( > It also reflects how many packages appear in sysfs, and this can > effect licensing of some kinds of software. That's just plain insanity and we should not let that affect our sysfs interfaces.
