linux-kernel - [PATCH 0/2] KVM: VMX: Tscdeadline timer emulation fastpath

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Date:   Tue, 21 Apr 2020 19:20:24 +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 0/2] 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):

5632.75ns -> 4559.25ns, 19%

kvm-unit-test/vmexit.flat:

w/o APICv, w/o advance timer:
tscdeadline_immed: 4780.75 -> 3851    19.4%
tscdeadline:       7474    -> 6528.5  12.7%

w/o APICv, w/ adaptive advance timer default -1:
tscdeadline_immed: 4845.75 -> 3930.5  18.9%
tscdeadline:       6048    -> 5871.75    3%

w/ APICv, w/o avanced timer:
tscdeadline_immed: 2919    -> 2467.75 15.5%
tscdeadline:       5661.75 -> 5188.25  8.4%

w/ APICv, w/ adaptive advance timer default -1:
tscdeadline_immed: 3018.5  -> 2561    15.2%
tscdeadline:       4663.75 -> 4626.5     1%

Tested-by: Haiwei Li <lihaiwei@...cent.com>
Cc: Haiwei Li <lihaiwei@...cent.com>

Wanpeng Li (2):
  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            |  20 ++------
 arch/x86/kvm/lapic.h            |  16 +++++++
 arch/x86/kvm/vmx/vmx.c          | 101 ++++++++++++++++++++++++++++++++++++++--
 arch/x86/kvm/x86.c              |  55 +++++++++++++++++++---
 5 files changed, 167 insertions(+), 28 deletions(-)

-- 
2.7.4