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SubjectRe: [PATCH v4 0/7] KVM: VMX: Tscdeadline timer emulation fastpath
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On 28/04/20 08:23, Wanpeng Li wrote:
> IPI and Timer cause the main vmexits in cloud environment observation,
> after single target IPI fastpath, let's optimize tscdeadline timer
> latency by introducing tscdeadline timer emulation fastpath, it will
> skip various KVM related checks when possible. i.e. after vmexit due
> to tscdeadline timer emulation, handle it and vmentry immediately
> without checking various kvm stuff when possible.
>
> Testing on SKX Server.
>
> cyclictest in guest(w/o mwait exposed, adaptive advance lapic timer is default -1):
>
> 5540.5ns -> 4602ns 17%
>
> kvm-unit-test/vmexit.flat:
>
> w/o avanced timer:
> tscdeadline_immed: 3028.5 -> 2494.75 17.6%
> tscdeadline: 5765.7 -> 5285 8.3%
>
> w/ adaptive advance timer default -1:
> tscdeadline_immed: 3123.75 -> 2583 17.3%
> tscdeadline: 4663.75 -> 4537 2.7%
>
> Tested-by: Haiwei Li <lihaiwei@tencent.com>
> Cc: Haiwei Li <lihaiwei@tencent.com>
>
> v3 -> v4:
> * fix bad indentation
> * rename CONT_RUN to REENTER_GUEST
> * rename kvm_need_cancel_enter_guest to kvm_vcpu_exit_request
> * rename EXIT_FASTPATH_CONT_RUN to EXIT_FASTPATH_REENTER_GUEST
> * introduce EXIT_FASTPATH_NOP
> * don't squish several stuffs to one patch
> * REENTER_GUEST be introduced with its first usage
> * introduce __handle_preemption_timer subfunction
>
> v2 -> v3:
> * skip interrupt notify and use vmx_sync_pir_to_irr before each cont_run
> * add from_timer_fn argument to apic_timer_expired
> * remove all kinds of duplicate codes
>
> v1 -> v2:
> * move more stuff from vmx.c to lapic.c
> * remove redundant checking
> * check more conditions to bail out CONT_RUN
> * not break AMD
> * not handle LVTT sepecial
> * cleanup codes
>
> Wanpeng Li (7):
> KVM: VMX: Introduce generic fastpath handler
> KVM: X86: Enable fastpath when APICv is enabled
> KVM: X86: Introduce more exit_fastpath_completion enum values
> KVM: X86: Introduce kvm_vcpu_exit_request() helper
> KVM: VMX: Optimize posted-interrupt delivery for timer fastpath
> KVM: X86: TSCDEADLINE MSR emulation fastpath
> KVM: VMX: Handle preemption timer fastpath
>
> arch/x86/include/asm/kvm_host.h | 3 ++
> arch/x86/kvm/lapic.c | 18 +++++++----
> arch/x86/kvm/svm/svm.c | 11 ++++---
> arch/x86/kvm/vmx/vmx.c | 66 +++++++++++++++++++++++++++++++++--------
> arch/x86/kvm/x86.c | 44 ++++++++++++++++++++-------
> arch/x86/kvm/x86.h | 3 +-
> virt/kvm/kvm_main.c | 1 +
> 7 files changed, 110 insertions(+), 36 deletions(-)
>

Queued all except 2, pending testing (and understanding the rationale
behind patch 2). I will post separately my version of patch 3.

Thanks,

Paolo

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