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

From: Wanpeng Li
Date: Tue Apr 28 2020 - 02:23:46 EST


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@xxxxxxxxxxx>
Cc: Haiwei Li <lihaiwei@xxxxxxxxxxx>

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(-)

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2.7.4