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

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Message-Id: <1588055009-12677-1-git-send-email-wanpengli@tencent.com>
Date:   Tue, 28 Apr 2020 14:23:22 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        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: [PATCH v4 0/7] KVM: VMX: Tscdeadline timer emulation fastpath

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(-)

-- 
2.7.4