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

Nicholas Piggin [off-list ref] writes:

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:

  usbcore: registered new interface driver usb-storage
  Disabling lock debugging due to kernel taint
  Severe Machine check interrupt [Not recovered]
    NIP [c0000000002a0c04]: kmem_cache_free+0x64/0x2c0
    Initiator: CPU
    Error type: Real address [Load/Store (foreign)]
  opal: Hardware platform error: Unrecoverable Machine Check exception
  CPU: 0 PID: 0 Comm: swapper/0 Tainted: G   M            4.13.0-rc2-gcc-6.3.1-00257-g26268bb39bff #543
  task: c0000000016b1200 task.stack: c00000000175c000
  NIP:  c0000000002a0c04 LR: c0000000001128ec CTR: c000000000112800
  REGS: c00000003fff7d80 TRAP: 0200   Tainted: G   M             (4.13.0-rc2-gcc-6.3.1-00257-g26268bb39bff)
  MSR:  9000000000209003 <SF,HV,EE,ME,RI,LE>  CR: 28002828  XER: 20000000
  CFAR: c0000000001128e8 DAR: c00a0000003c3ce0 DSISR: 00000008 SOFTE: 1 
  GPR00: c0000000001128ec c00000000175f7b0 c000000001760500 c0000000f001a000 
  GPR04: c0000000f0f37f00 0000000000000003 00000000000220c3 0000000000000000 
  GPR08: 0000000000000000 00000000003c3cc0 c0000000017e7758 0000000000000000 
  GPR12: c000000000112800 c00000000fff0000 c000000000112800 c0000000f0f37f90 
  GPR16: c00000000175c000 c00000000175c000 0000000000000001 c0000000016d7900 
  GPR20: c00000000179ba98 7fffffffffffffff c00000000175c000 0000000000000000 
  GPR24: c00000000017a8c0 000000000000000a c0000000016d8a00 c00000000175f8d0 
  GPR28: c0000000001128ec c0000000f0f37f00 c00a0000003c3cc0 c0000000f001a000 
  NIP [c0000000002a0c04] kmem_cache_free+0x64/0x2c0
  LR [c0000000001128ec] put_cred_rcu+0xec/0x140
  Call Trace:
  [c00000000175f7b0] [c00000000175f800] init_thread_union+0x3800/0x4000 (unreliable)
  [c00000000175f840] [c0000000001128ec] put_cred_rcu+0xec/0x140
  [c00000000175f8b0] [c00000000017a908] rcu_process_callbacks+0x438/0x6a0
  [c00000000175f980] [c0000000000e5e28] __do_softirq+0x198/0x310
  [c00000000175fa70] [c0000000000e6248] irq_exit+0xf8/0x140
  [c00000000175fa90] [c000000000023710] timer_interrupt+0xa0/0xe0
  [c00000000175fac0] [c000000000008fcc] decrementer_common+0x11c/0x120
  --- interrupt: 901 at replay_interrupt_return+0x0/0x4
      LR = arch_local_irq_restore.part.1+0x84/0xb0
  [c00000000175fdb0] [c00000000175c000] init_thread_union+0x0/0x4000 (unreliable)
  [c00000000175fdd0] [c00000000001cde0] arch_cpu_idle+0xe0/0x140
  [c00000000175fe00] [c0000000007f4f44] default_idle_call+0x44/0x84
  [c00000000175fe20] [c000000000142e54] do_idle+0x254/0x320
  [c00000000175fe90] [c000000000143280] cpu_startup_entry+0x30/0x40
  [c00000000175fec0] [c00000000000d2d8] rest_init+0x2f8/0x320
  [c00000000175ff00] [c000000001000d74] start_kernel+0x510/0x52c
  [c00000000175ff90] [c00000000000ab70] start_here_common+0x1c/0x4ac
  Instruction dump:
  60000000 e9230008 71280100 40820170 2fbf0000 419e013c 3d420008 394a7258 
  7bbe8502 7bc93664 ebca0000 7fde4a14 <e93e0020> 712a0001 40820234 e93f0008 
  [    1.217346467,0] OPAL: Reboot requested due to Platform error.
  [    1.217351582,3] OPAL: failed to log an error
  [    1.217358188,5] OPAL: Reboot request...


I'll just drop it for now.

cheers