Re: [PATCH v3 4/4] powerpc/64s: idle ESL=0 stop can avoid MSR and save/restore overhead

On Wed, 30 Aug 2017 21:25:59 +1000
Michael Ellerman [off-list ref] wrote:

Nicholas Piggin [off-list ref] writes:

quoted

When stop is executed with EC=ESL=0, it appears to execute like a
normal instruction (resuming from NIP when woken by interrupt).
So all the save/restore handling can be avoided completely. In
particular NV GPRs do not have to be saved, and MSR does not have
to be switched back to kernel MSR.

So move the test for "lite" sleep states out to power9_idle_stop.

Reviewed-by: Gautham R. Shenoy <redacted>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kernel/idle_book3s.S | 35 ++++++++++++++++++++++++-----------
 1 file changed, 24 insertions(+), 11 deletions(-)  

This is blowing up for me on mambo:

Oh this is a known bug in mambo that does not match the hardware.

You need >= Mambo.7.8.21, or this firmware patch to work around
the issue for old mambos.

mambo.git 58d3162f4d6204fc077ff4a6ba47e4d1e19d5120

https://lists.ozlabs.org/pipermail/skiboot/2017-August/008768.html

Thanks,
Nick