On Fri, Mar 11, 2022 at 05:21:21PM +0000, Szabolcs Nagy wrote: > The 02/25/2022 16:58, Mark Brown wrote: > i would s/SVE vector/streaming mode SVE vector/ Done. > > +* On creation fork() or clone() the newly created process will have PSTATE.SM > > + and PSTATE.ZA cleared. > is there a reason why fork() clears ZA? > i think this is a minor issue, but the usual expectation is that > on thread creation thread local state is reset in the child, but > in a forked child the state is the same as in the parent (where > ZA is preserved according to the first rule). It was partly consistency with SM and the SVE state (though that is also covered by just being in a system call unlike ZA) and partly concerns about what happens if the fork() happens in library code which isn't SME aware - it would end up carrying around a copy of ZA with associated power and performance impacts if it doesn't exec(). Overall it seemed like there would to be less potential for unpleasant surprises if we consistently discard the data. That's not a *super* strongly held opinion though, we could switch to preserving whenever we preserve TPIDR2.
Attachment:
signature.asc
Description: PGP signature
_______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
