linux-kernel - Re: [PATCH v4 0/7] KVM: VMX: Tscdeadline timer emulation fastpath

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Date:   Mon, 4 May 2020 19:22:36 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Haiwei Li <lihaiwei@...cent.com>
Subject: Re: [PATCH v4 0/7] KVM: VMX: Tscdeadline timer emulation fastpath

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@...cent.com>
> Cc: Haiwei Li <lihaiwei@...cent.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