Re: [PATCH v2 00/60] KVM: PPC: Book3S HV P9: entry/exit optimisations

[Athira Rajeev <atrajeev@linux.vnet.ibm.com>]

> On 11-Aug-2021, at 9:30 PM, Nicholas Piggin <npiggin@gmail.com> wrote:
> 
> This reduces radix guest full entry/exit latency on POWER9 and POWER10
> by 2x.
> 
> Nested HV guests should see smaller improvements in their L1 entry/exit,
> but this is also combined with most L0 speedups also applying to nested
> entry. nginx localhost throughput test in a SMP nested guest is improved
> about 10% (in a direct guest it doesn't change much because it uses XIVE
> for IPIs) when L0 and L1 are patched.
> 
> It does this in several main ways:
> 
> - Rearrange code to optimise SPR accesses. Mainly, avoid scoreboard
>  stalls.
> 
> - Test SPR values to avoid mtSPRs where possible. mtSPRs are expensive.
> 
> - Reduce mftb. mftb is expensive.
> 
> - Demand fault certain facilities to avoid saving and/or restoring them
>  (at the cost of fault when they are used, but this is mitigated over
>  a number of entries, like the facilities when context switching 
>  processes). PM, TM, and EBB so far.
> 
> - Defer some sequences that are made just in case a guest is interrupted
>  in the middle of a critical section to the case where the guest is
>  scheduled on a different CPU, rather than every time (at the cost of
>  an extra IPI in this case). Namely the tlbsync sequence for radix with
>  GTSE, which is very expensive.
> 
> - Reduce locking, barriers, atomics related to the vcpus-per-vcore > 1
>  handling that the P9 path does not require.
> 
> Changes since v1:
> - Verified DPDES changes still work with msgsndp SMT emulation.
> - Fixed HMI handling bug.
> - Split softpatch handling fixes into smaller pieces.
> - Rebased with Fabiano's latest HV sanitising patches.
> - Fix TM demand faulting bug causing nested guest TM tests to TM Bad
>  Thing the host in rare cases.
> - Re-name new "pmu=" command line option to "pmu_override=" and update
>  documentation wording.

Hi Nick,

For the PMU related changes,

Reviewed-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>

Thanks
Athira
> - Add default=y config option rather than unconditionally removing the
>  L0 nested PMU workaround.
> - Remove unnecessary MSR[RI] updates in entry/exit. Down to about 4700
>  cycles now.
> - Another bugfix from Alexey's testing.
> 
> Changes since RFC:
> - Rebased with Fabiano's HV sanitising patches at the front.
> - Several demand faulting bug fixes mostly relating to nested guests.
> - Removed facility demand-faulting from L0 nested entry/exit handler.
>  Demand faulting is still done in the L1, but not the L0. The reason
>  is to reduce complexity (although it's only a small amount of
>  complexity), reduce demand faulting overhead that may require several
> 
> Fabiano Rosas (3):
>  KVM: PPC: Book3S HV Nested: Sanitise vcpu registers
>  KVM: PPC: Book3S HV Nested: Stop forwarding all HFUs to L1
>  KVM: PPC: Book3S HV Nested: save_hv_return_state does not require trap
>    argument
> 
> Nicholas Piggin (57):
>  KVM: PPC: Book3S HV: Initialise vcpu MSR with MSR_ME
>  KVM: PPC: Book3S HV: Remove TM emulation from POWER7/8 path
>  KVM: PPC: Book3S HV P9: Fixes for TM softpatch interrupt NIP
>  KVM: PPC: Book3S HV Nested: Fix TM softpatch HFAC interrupt emulation
>  KVM: PPC: Book3S HV Nested: Make nested HFSCR state accessible
>  KVM: PPC: Book3S HV Nested: Reflect guest PMU in-use to L0 when guest
>    SPRs are live
>  powerpc/64s: Remove WORT SPR from POWER9/10
>  KMV: PPC: Book3S HV P9: Use set_dec to set decrementer to host
>  KVM: PPC: Book3S HV P9: Use host timer accounting to avoid decrementer
>    read
>  KVM: PPC: Book3S HV P9: Use large decrementer for HDEC
>  KVM: PPC: Book3S HV P9: Reduce mftb per guest entry/exit
>  powerpc/time: add API for KVM to re-arm the host timer/decrementer
>  KVM: PPC: Book3S HV: POWER10 enable HAIL when running radix guests
>  powerpc/64s: Keep AMOR SPR a constant ~0 at runtime
>  KVM: PPC: Book3S HV: Don't always save PMU for guest capable of
>    nesting
>  powerpc/64s: Always set PMU control registers to frozen/disabled when
>    not in use
>  powerpc/64s: Implement PMU override command line option
>  KVM: PPC: Book3S HV P9: Implement PMU save/restore in C
>  KVM: PPC: Book3S HV P9: Factor PMU save/load into context switch
>    functions
>  KVM: PPC: Book3S HV P9: Demand fault PMU SPRs when marked not inuse
>  KVM: PPC: Book3S HV P9: Factor out yield_count increment
>  KVM: PPC: Book3S HV: CTRL SPR does not require read-modify-write
>  KVM: PPC: Book3S HV P9: Move SPRG restore to restore_p9_host_os_sprs
>  KVM: PPC: Book3S HV P9: Reduce mtmsrd instructions required to save
>    host SPRs
>  KVM: PPC: Book3S HV P9: Improve mtmsrd scheduling by delaying MSR[EE]
>    disable
>  KVM: PPC: Book3S HV P9: Add kvmppc_stop_thread to match
>    kvmppc_start_thread
>  KVM: PPC: Book3S HV: Change dec_expires to be relative to guest
>    timebase
>  KVM: PPC: Book3S HV P9: Move TB updates
>  KVM: PPC: Book3S HV P9: Optimise timebase reads
>  KVM: PPC: Book3S HV P9: Avoid SPR scoreboard stalls
>  KVM: PPC: Book3S HV P9: Only execute mtSPR if the value changed
>  KVM: PPC: Book3S HV P9: Juggle SPR switching around
>  KVM: PPC: Book3S HV P9: Move vcpu register save/restore into functions
>  KVM: PPC: Book3S HV P9: Move host OS save/restore functions to
>    built-in
>  KVM: PPC: Book3S HV P9: Move nested guest entry into its own function
>  KVM: PPC: Book3S HV P9: Move remaining SPR and MSR access into low
>    level entry
>  KVM: PPC: Book3S HV P9: Implement TM fastpath for guest entry/exit
>  KVM: PPC: Book3S HV P9: Switch PMU to guest as late as possible
>  KVM: PPC: Book3S HV P9: Restrict DSISR canary workaround to processors
>    that require it
>  KVM: PPC: Book3S HV P9: More SPR speed improvements
>  KVM: PPC: Book3S HV P9: Demand fault EBB facility registers
>  KVM: PPC: Book3S HV P9: Demand fault TM facility registers
>  KVM: PPC: Book3S HV P9: Use Linux SPR save/restore to manage some host
>    SPRs
>  KVM: PPC: Book3S HV P9: Comment and fix MMU context switching code
>  KVM: PPC: Book3S HV P9: Test dawr_enabled() before saving host DAWR
>    SPRs
>  KVM: PPC: Book3S HV P9: Don't restore PSSCR if not needed
>  KVM: PPC: Book3S HV P9: Avoid tlbsync sequence on radix guest exit
>  KVM: PPC: Book3S HV Nested: Avoid extra mftb() in nested entry
>  KVM: PPC: Book3S HV P9: Improve mfmsr performance on entry
>  KVM: PPC: Book3S HV P9: Optimise hash guest SLB saving
>  KVM: PPC: Book3S HV P9: Avoid changing MSR[RI] in entry and exit
>  KVM: PPC: Book3S HV P9: Add unlikely annotation for !mmu_ready
>  KVM: PPC: Book3S HV P9: Avoid cpu_in_guest atomics on entry and exit
>  KVM: PPC: Book3S HV P9: Remove most of the vcore logic
>  KVM: PPC: Book3S HV P9: Tidy kvmppc_create_dtl_entry
>  KVM: PPC: Book3S HV P9: Stop using vc->dpdes
>  KVM: PPC: Book3S HV P9: Remove subcore HMI handling
> 
> .../admin-guide/kernel-parameters.txt         |   8 +
> arch/powerpc/include/asm/asm-prototypes.h     |   5 -
> arch/powerpc/include/asm/kvm_asm.h            |   1 +
> arch/powerpc/include/asm/kvm_book3s.h         |   6 +
> arch/powerpc/include/asm/kvm_book3s_64.h      |   6 +-
> arch/powerpc/include/asm/kvm_host.h           |   7 +-
> arch/powerpc/include/asm/kvm_ppc.h            |   1 +
> arch/powerpc/include/asm/pmc.h                |   7 +
> arch/powerpc/include/asm/reg.h                |   3 +-
> arch/powerpc/include/asm/switch_to.h          |   2 +
> arch/powerpc/include/asm/time.h               |  19 +-
> arch/powerpc/kernel/cpu_setup_power.c         |  12 +-
> arch/powerpc/kernel/dt_cpu_ftrs.c             |   8 +-
> arch/powerpc/kernel/process.c                 |  32 +
> arch/powerpc/kernel/time.c                    |  54 +-
> arch/powerpc/kvm/Kconfig                      |  15 +
> arch/powerpc/kvm/book3s_64_mmu_radix.c        |   4 +
> arch/powerpc/kvm/book3s_hv.c                  | 890 ++++++++++--------
> arch/powerpc/kvm/book3s_hv.h                  |  41 +
> arch/powerpc/kvm/book3s_hv_builtin.c          |   2 +
> arch/powerpc/kvm/book3s_hv_hmi.c              |   7 +-
> arch/powerpc/kvm/book3s_hv_interrupts.S       |  13 +-
> arch/powerpc/kvm/book3s_hv_nested.c           | 109 ++-
> arch/powerpc/kvm/book3s_hv_p9_entry.c         | 817 +++++++++++++---
> arch/powerpc/kvm/book3s_hv_ras.c              |  54 ++
> arch/powerpc/kvm/book3s_hv_rmhandlers.S       | 115 +--
> arch/powerpc/kvm/book3s_hv_tm.c               |  61 +-
> arch/powerpc/mm/book3s64/radix_pgtable.c      |  15 -
> arch/powerpc/perf/core-book3s.c               |  35 +
> arch/powerpc/platforms/powernv/idle.c         |  10 +-
> 30 files changed, 1589 insertions(+), 770 deletions(-)
> create mode 100644 arch/powerpc/kvm/book3s_hv.h
> 
> -- 
> 2.23.0
>