On Mon, Feb 25, 2019 at 5:51 PM Keith Busch <keith.busch@xxxxxxxxx> wrote: > > On Sun, Feb 24, 2019 at 08:59:45PM +0100, Rafael J. Wysocki wrote: > > On Fri, Feb 22, 2019 at 7:48 PM Keith Busch <keith.busch@xxxxxxxxx> wrote: > > > If I do it the other way around, that's going to make HMEM_REPORTING > > > complicated if a non-ACPI implementation wants to report HMEM > > > properties. > > > > But the mitigations that Dave was talking about get in the way, don't they? > > > > Say there is another Kconfig option,CACHE_MITIGATIONS, to enable them. > > Then you want ACPI_HMAT to be set when that it set and you also want > > ACPI_HMAT to be set when HMEM_REPORTING and ACPI_NUMA are both set. > > > > OTOH, you may not want HMEM_REPORTING to be set when CACHE_MITIGATIONS > > is set, but that causes ACPI_HMAT to be set and which means that > > ACPI_HMAT alone will not be sufficient to determine the > > HMEM_REPORTING value. > > I can't think of when we'd want to suppress reporting these attributes > to user space, but I can split HMAT enabling so it doesn't depend on > HMEM_REPORTING just in case there really is an in-kernel user that > definitely does not want the same attributes exported. I'd rather simplify HMAT enabling than make it more complicated, so splitting it would be worse than what you have already IMO. > > Now, if you prompt for HMEM_REPORTING and make it depend on ACPI_NUMA, > > then ACPI_HMAT can be selected by that (regardless of the > > CACHE_MITIGATIONS value). > > > > And if someone wants to use HMEM_REPORTING without ACPI_NUMA, it can > > be made depend on whatever new option is there for that non-ACPI > > mechanism. > > > > There might be a problem if someone wanted to enable the alternative > > way of HMEM_REPORTING if ACPI_NUMA was set (in which case HMAT would > > have to be ignored even if it was present), but in that case there > > would need to be an explicit way to choose between HMAT and non-HMAT > > anyway. > > > > In any case, I prefer providers to be selected by consumers and not > > the other way around, in case there are multiple consumers for one > > provider. > > Well, the HMEM_REPORTING fundamentally has no dependency on any of these > things and I've put some effort into making this part provider agnostic. Which I agree with. > I will change it if this concern is gating acceptance, but I don't > think it's as intuitive for generic interfaces to be the selector for > implementation specific providers. That is sort of a chicken-and-egg issue about what is more fundamental that could be discussed forever. :-) My original point was that if you regard ACPI_HMAT as the more fundamental thing, then you should prompt for it and select HMEM_REPORTING automatically from there. Or the other way around if you regard HMEM_REPORTING as more fundamental. Prompting for both of them may lead to issues. As long as that is taken into account, I'm basically fine with any of the two choices.
