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

On Fri, 01 Sep 2017 19:39:41 +1000
Michael Ellerman [off-list ref] wrote:

Nicholas Piggin [off-list ref] writes:

quoted

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

quoted

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.  

As discussed elsewhere this still breaks on new mambo with more than one
CPU. So I've dropped it for now.

This now seems to be properly fixed in mambo with commit 11783550ee11.

Skiboot also has a patch merged which disables the problematic state on
mambo so older versions won't crash.

d2a24406a49 ("idle: disable stop*_lite POWER9 idle states for Mambo platform")

So this could be re-applied now.

Thanks,
Nick