[PATCH v2 2/2] powerpc/64s: reimplement book3s idle code in C

[Nicholas Piggin]

On Fri, 10 Aug 2018 16:42:49 +1000
Nicholas Piggin <npiggin at gmail.com> wrote:

> Reimplement Book3S idle code in C, moving POWER7/8/9 implementation
> speific HV idle code to the powernv platform code.
> 
> Book3S assembly stubs are kept in common code and used only to save
> the stack frame and non-volatile GPRs before executing architected
> idle instructions, and restoring the stack and reloading GPRs then
> returning to C after waking from idle.
> 
> The complex logic dealing with threads and subcores, locking, SPRs,
> HMIs, timebase resync, etc., is all done in C which makes it more
> maintainable.
> 
> This is not a strict translation to C code, there are some
> significant differences:
> 
> - Idle wakeup no longer uses the ->cpu_restore call to reinit SPRs,
>   but saves and restores them itself.
> 
> - The optimisation where EC=ESL=0 idle modes did not have to save GPRs
>   or change MSR is restored, because it's now simple to do. ESL=1
>   sleeps that do not lose GPRs can use this optimization too.
> 
> - KVM secondary entry and cede is now more of a call/return style
>   rather than branchy. nap_state_lost is not required because KVM
>   always returns via NVGPR restoring path.
> 
> Reviewed-by: Gautham R. Shenoy <ego at linux.vnet.ibm.com>
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> 
> Left to do:
> - KVM could use more review, it's pretty tricky. Not sure if what
>   I'm doing with the emergency stack is kosher. But it runs pretty fine
>   here with a POWER9 SMP+SMT guest. Possible to streamline

That should be POWER8. POWER9 radix on hash with dependent threads
mode also seems to work okay.

Thanks,
Nick