On Fri, May 31, 2019 at 04:54:20PM +0200, Jiri Kosina wrote: > On Fri, 31 May 2019, Andy Lutomirski wrote: > > > For that matter, what actually happens if we get an SMI while halted? > > Does RSM go directly to sleep or does it re-fetch the HLT? > > Our mails just crossed, I replied to Josh's mwait() proposal patch a > minute ago.
Good catch. I agree that mwait seems unsafe across resume and my patch is bogus. Andy, in the short term it sounds like you're proposing to make native_play_dead() use hlt_play_dead() unconditionally. Right? That would simplify things and also would fix Jiri's bug I think. The only question I'd have is if we have data on the power savings difference between hlt and mwait. mwait seems to wake up on a lot of different conditions which might negate its deeper sleep state. Andy, for your long term idea to use INIT IPI, I wonder if that would work with SMT siblings? Specifically I wonder about the Intel issue that requires siblings to have CR4.MCE set. -- Josh
