Re: [PATCH v3 0/6] IPI virtualization support for VM

Zeng Guang
2021-08-06T05:37:09Z

On 8/6/2021 1:03 AM, Jim Mattson wrote:
> On Thu, Aug 5, 2021 at 8:38 AM Zeng Guang <guang.zeng@intel.com> wrote:
>
> Current IPI process in guest VM will virtualize the writing to interrupt
> command register(ICR) of the local APIC which will cause VM-exit anyway
> on source vCPU. Frequent VM-exit could induce much overhead accumulated
> if running IPI intensive task.
>
> IPI virtualization as a new VT-x feature targets to eliminate VM-exits
> when issuing IPI on source vCPU. It introduces a new VM-execution
> control - "IPI virtualization"(bit4) in the tertiary processor-based
> VM-exection controls and a new data structure - "PID-pointer table
> VM-execution
>> address" and "Last PID-pointer index" referenced by the VMCS. When "IPI
>> virtualization" is enabled, processor emulateds following kind of writes
> emulates
> to APIC registers that would send IPIs, moreover without causing VM-exits.
> - Memory-mapped ICR writes
> - MSR-mapped ICR writes
> - SENDUIPI execution
>
> This patch series implement IPI virtualization support in KVM.
> implements
>> Patches 1-4 add tertiary processor-based VM-execution support
>> framework.
>>
>> Patch 5 implement interrupt dispatch support in x2APIC mode with
> implements
>> APIC-write VM exit. In previous platform, no CPU would produce
>> APIC-write VM exit with exit qulification 300H when the "virtual x2APIC
> qualification
>> mode" VM-execution control was 1.
>>
>> Patch 6 implement IPI virtualization related function including
>> feature enabling through tertiary processor-based VM-execution in
>> various scenario of VMCS configuration, PID table setup in vCPU creation
> scenarios
>> and vCPU block consideration.
>>
>> Document for IPI virtualization is now available at the latest "Intel
>> Architecture Instruction Set Extensions Programming Reference".
>>
>> Document Link:
>> https://software.intel.com/content/www/us/en/develop/download/intel-architecture-instruction-set-extensions-programming-reference.html
>>
>> We did experiment to measure average time sending IPI from source vCPU
>> to the target vCPU completing the IPI handling by kvm unittest w/ and
>> w/o IPI virtualization. When IPI virtualizatin enabled, it will reduce
> virtualization
>> 22.21% and 15.98% cycles consuming in xAPIC mode and x2APIC mode
>> respectly.
> respectively
>> KMV unittest:vmexit/ipi, 2 vCPU, AP was modified to run in idle loop
> KVM

Thanks for your all corrections.

>> instead of halt to ensure no VM exit impact on target vCPU.
> Are you going to post the kvm-init-test changes?

We modified unit test common code specific for the IPIv test purpose,
currently no plan to post those changes to kvm-uint-tests.
>> Cycles of IPI
>> xAPIC mode x2APIC mode
>> test w/o IPIv w/ IPIv w/o IPIv w/ IPIv
>> 1 6106 4816 4265 3768
>> 2 6244 4656 4404 3546
>> 3 6165 4658 4233 3474
>> 4 5992 4710 4363 3430
>> 5 6083 4741 4215 3551
>> 6 6238 4904 4304 3547
>> 7 6164 4617 4263 3709
>> 8 5984 4763 4518 3779
>> 9 5931 4712 4645 3667
>> 10 5955 4530 4332 3724
>> 11 5897 4673 4283 3569
>> 12 6140 4794 4178 3598
>> 13 6183 4728 4363 3628
>> 14 5991 4994 4509 3842
>> 15 5866 4665 4520 3739
>> 16 6032 4654 4229 3701
>> 17 6050 4653 4185 3726
>> 18 6004 4792 4319 3746
>> 19 5961 4626 4196 3392
>> 20 6194 4576 4433 3760
>>
>> Average cycles 6059 4713.1 4337.85 3644.8
>> %Reduction -22.21% -15.98%
>>
>> --------------------------------------
>> IPI microbenchmark:
>> (https://lore.kernel.org/kvm/20171219085010.4081-1-ynorov@caviumnetworks.com)
>>
>> 2 vCPUs, 1:1 pin vCPU to pCPU, guest VM runs with idle=poll, x2APIC mode
> For dedicated CPUs, we would just disable the MONITOR/MWAIT intercepts
> and expose MONITOR/MWAIT to the guest. We would not recommend that
> anyone use idle=poll.
OK. We thought that straightforward way to make guest keep running in
idle without side
effect of VM exit and other factors, so used idle=poll for test.
>> Result with IPIv enabled:
>>
>> Dry-run: 0, 272798 ns
>> Self-IPI: 5094123, 11114037 ns
>> Normal IPI: 131697087, 173321200 ns
>> Broadcast IPI: 0, 155649075 ns
>> Broadcast lock: 0, 161518031 ns
>>
>> Result with IPIv disabled:
>>
>> Dry-run: 0, 272766 ns
>> Self-IPI: 5091788, 11123699 ns
>> Normal IPI: 145215772, 174558920 ns
>> Broadcast IPI: 0, 175785384 ns
>> Broadcast lock: 0, 149076195 ns
>>
>>
>> As IPIv can benefit unicast IPI to other CPU, Noraml IPI test case gain
> Normal
>> about 9.73% time saving on average out of 15 test runs when IPIv is
>> enabled.
> Can you share the CDFs?
Normal IPI statistics:
test            w/o IPIv  (unit:ns)        w/ IPIv
(unit:ns)
1                153346049 140907046
2                147218648 141660618
3                145215772 117890672
4                146621682 136430470
5                144821472 136199421
6                144704378 131676928
7                141403224 131697087
8                144775766 125476250
9                140658192 137263330
10              144768626 138593127
11              145166679 131946752
12              145020451 116852889
13              148161353 131406280
14              148378655 130174353
15              148903652 127969674
>> w/o IPIv w/ IPIv
>> Normal IPI: 145944306.6 ns 131742993.1 ns
>> %Reduction -9.73%
>>
>> --------------------------------------
>> hackbench:
>>
>> 8 vCPUs, guest VM free run, x2APIC mode
>> ./hackbench -p -l 100000
>>
>> w/o IPIv w/ IPIv
>> Time: 91.887 74.605
>> %Reduction: -18.808%
>>
>> 96 vCPUs, guest VM free run, x2APIC mode
>> ./hackbench -p -l 1000000
>>
>> w/o IPIv w/ IPIv
>> Time: 287.504 235.185
>> %Reduction: -18.198%
>>
>> --------------------------------------
>>
>> v2 -> v3:
>> 1. Misc change on tertiary execution control
>> definition and capability setup
>> 2. Alternative to get tertiary execution
>> control configuration
>>
>> v1 -> v2:
>> 1. Refine the IPIv enabling logic for VM.
>> Remove ipiv_active definition per vCPU.
>>
>> Gao Chao (1):
>> KVM: VMX: enable IPI virtualization
>>
>> Robert Hoo (4):
>> x86/feat_ctl: Add new VMX feature, Tertiary VM-Execution control
>> KVM: VMX: Extend BUILD_CONTROLS_SHADOW macro to support 64-bit
>> variation
>> KVM: VMX: Detect Tertiary VM-Execution control when setup VMCS config
>> KVM: VMX: dump_vmcs() reports tertiary_exec_control field as well
>>
>> Zeng Guang (1):
>> KVM: x86: Support interrupt dispatch in x2APIC mode with APIC-write VM
>> exit
>>
>> arch/x86/include/asm/msr-index.h | 1 +
>> arch/x86/include/asm/vmx.h | 11 +++
>> arch/x86/include/asm/vmxfeatures.h | 5 +-
>> arch/x86/kernel/cpu/feat_ctl.c | 11 ++-
>> arch/x86/kvm/lapic.c | 9 ++-
>> arch/x86/kvm/vmx/capabilities.h | 14 ++++
>> arch/x86/kvm/vmx/evmcs.c | 2 +
>> arch/x86/kvm/vmx/evmcs.h | 1 +
>> arch/x86/kvm/vmx/posted_intr.c | 22 ++++--
>> arch/x86/kvm/vmx/vmcs.h | 1 +
>> arch/x86/kvm/vmx/vmx.c | 114 +++++++++++++++++++++++++++--
>> arch/x86/kvm/vmx/vmx.h | 27 ++++---
>> 12 files changed, 193 insertions(+), 25 deletions(-)
>>
>> --
>> 2.25.1
>>