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author | Nicholas Piggin <npiggin@gmail.com> | 2019-04-13 00:30:52 +1000 |
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committer | Michael Ellerman <mpe@ellerman.id.au> | 2019-04-30 22:37:48 +1000 |
commit | 10d91611f426d4bafd2a83d966c36da811b2f7ad (patch) | |
tree | e455d47497c64533f4537290dae97baae10d0340 /arch/powerpc/kernel/exceptions-64s.S | |
parent | c1fe190c06723322f2dfac31d3b982c581e434ef (diff) | |
download | linux-10d91611f426d4bafd2a83d966c36da811b2f7ad.tar.bz2 |
powerpc/64s: Reimplement book3s idle code in C
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.
- KVM secondary wakeup from offline sequence is moved entirely into
the offline wakeup, which avoids a hwsync in the normal idle wakeup
path.
Performance measured with context switch ping-pong on different
threads or cores, is possibly improved a small amount, 1-3% depending
on stop state and core vs thread test for shallow states. Deep states
it's in the noise compared with other latencies.
KVM improvements:
- Idle sleepers now always return to caller rather than branch out
to KVM first.
- This allows optimisations like very fast return to caller when no
state has been lost.
- KVM no longer requires nap_state_lost because it controls NVGPR
save/restore itself on the way in and out.
- The heavy idle wakeup KVM request check can be moved out of the
normal host idle code and into the not-performance-critical offline
code.
- KVM nap code now returns from where it is called, which makes the
flow a bit easier to follow.
Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Squash the KVM changes in]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/kernel/exceptions-64s.S')
-rw-r--r-- | arch/powerpc/kernel/exceptions-64s.S | 23 |
1 files changed, 14 insertions, 9 deletions
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index a5b8fbae56a0..6247b5bbfa5c 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -120,7 +120,9 @@ EXC_VIRT_NONE(0x4000, 0x100) mfspr r10,SPRN_SRR1 ; \ rlwinm. r10,r10,47-31,30,31 ; \ beq- 1f ; \ - cmpwi cr3,r10,2 ; \ + cmpwi cr1,r10,2 ; \ + mfspr r3,SPRN_SRR1 ; \ + bltlr cr1 ; /* no state loss, return to idle caller */ \ BRANCH_TO_C000(r10, system_reset_idle_common) ; \ 1: \ KVMTEST_PR(n) ; \ @@ -144,8 +146,11 @@ TRAMP_KVM(PACA_EXNMI, 0x100) #ifdef CONFIG_PPC_P7_NAP EXC_COMMON_BEGIN(system_reset_idle_common) - mfspr r12,SPRN_SRR1 - b pnv_powersave_wakeup + /* + * This must be a direct branch (without linker branch stub) because + * we can not use TOC at this point as r2 may not be restored yet. + */ + b idle_return_gpr_loss #endif /* @@ -427,17 +432,17 @@ EXC_COMMON_BEGIN(machine_check_idle_common) * Then decrement MCE nesting after finishing with the stack. */ ld r3,_MSR(r1) + ld r4,_LINK(r1) lhz r11,PACA_IN_MCE(r13) subi r11,r11,1 sth r11,PACA_IN_MCE(r13) - /* Turn off the RI bit because SRR1 is used by idle wakeup code. */ - /* Recoverability could be improved by reducing the use of SRR1. */ - li r11,0 - mtmsrd r11,1 - - b pnv_powersave_wakeup_mce + mtlr r4 + rlwinm r10,r3,47-31,30,31 + cmpwi cr1,r10,2 + bltlr cr1 /* no state loss, return to idle caller */ + b idle_return_gpr_loss #endif /* * Handle machine check early in real mode. We come here with |