[PATCH v2 00/60] KVM: PPC: Book3S HV P9: entry/exit optimisations
Athira Rajeev
atrajeev at linux.vnet.ibm.com
Mon Aug 16 18:41:51 AEST 2021
> On 11-Aug-2021, at 9:30 PM, Nicholas Piggin <npiggin at 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 at 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
>
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