On Wed, 28 Mar 2018, Laurent Dufour wrote: > > Putting this in mm/Kconfig is definitely the right way to go about it > > instead of any generic option in arch/*. > > > > My question, though, was making this configurable by the user: > > > > config SPECULATIVE_PAGE_FAULT > > bool "Speculative page faults" > > depends on X86_64 || PPC > > default y > > help > > .. > > > > It's a question about whether we want this always enabled on x86_64 and > > power or whether the user should be able to disable it (right now they > > can't). With a large feature like this, you may want to offer something > > simple (disable CONFIG_SPECULATIVE_PAGE_FAULT) if someone runs into > > regressions. > > I agree, but I think it would be important to get the per architecture > enablement to avoid complex check here. For instance in the case of powerPC > this is only supported for PPC_BOOK3S_64. > > To avoid exposing such per architecture define here, what do you think about > having supporting architectures setting ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT > and the SPECULATIVE_PAGE_FAULT depends on this, like this: > > In mm/Kconfig: > config SPECULATIVE_PAGE_FAULT > bool "Speculative page faults" > depends on ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT && SMP > default y > help > ... > > In arch/powerpc/Kconfig: > config PPC > ... > select ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT if PPC_BOOK3S_64 > > In arch/x86/Kconfig: > config X86_64 > ... > select ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT > > Looks good to me! It feels like this will add more assurance that if things regress for certain workloads that it can be disabled. I don't feel strongly about the default value, I'm ok with it being enabled by default.
