Hi! On Tue, Sep 20, 2022 at 12:01:47AM +1000, Nicholas Piggin wrote: > Update the 64s GENERIC_CPU option. POWER4 support has been dropped, so > make that clear in the option name.
AFAIR the minimum now is POWER4+ (ISA 2.01), not POWER5 (ISA 2.02). > -mtune= before power8 is dropped because the minimum gcc version > supports power8, and tuning is made consistent between big and little > endian. Tuning for p8 on e.g. 970 gives quite bad results. No idea if anyone cares, but this is a serious regression if so. > Big endian drops -mcpu=power4 in favour of power5. Effectively the > minimum compiler version means power5 was always being selected here, > so this should not change anything. 970 / G5 code generation does not > seem to have been a problem with -mcpu=power5, but it's possible we > should go back to power4 to be really safe. Yes, -mcpu=power5 code does *not* run on 970, if you are unlucky enough that the compiler does something smart with popcntb (the sole non-float insn new on p5, not counting hrfid). > +# -mcpu=power5 should generate 970 compatible kernel code It doesn't. Even if it did, it would need more explanation! Segher