On Mon, 19 Jul 2021 at 15:26, Zeng Guang <guang.zeng@xxxxxxxxx> wrote: > > On 7/16/2021 5:25 PM, Wanpeng Li wrote: > > On Fri, 16 Jul 2021 at 15:14, Zeng Guang <guang.zeng@xxxxxxxxx> 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 > >> address" and "Last PID-pointer index" referenced by the VMCS. When "IPI > >> virtualization" is enabled, processor emulateds following kind of writes > >> 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. > >> > >> Patches 1-3 add tertiary processor-based VM-execution support > >> framework. > >> > >> Patch 4 implement interrupt dispatch support in x2APIC mode with > >> APIC-write VM exit. In previous platform, no CPU would produce > >> APIC-write VM exit with exit qulification 300H when the "virtual x2APIC > >> mode" VM-execution control was 1. > >> > >> Patch 5 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 > >> 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 > >> 22.21% and 15.98% cycles comsuming in xAPIC mode and x2APIC mode > >> respectly. > >> > >> KMV unittest:vmexit/ipi, 2 vCPU, AP runs without halt to ensure no VM > >> exit impact on target vCPU. > >> > >> 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% > > Commit a9ab13ff6e (KVM: X86: Improve latency for single target IPI > > fastpath) mentioned that the whole ipi fastpath feature reduces the > > latency from 4238 to 3293 around 22.3% on SKX server, why your IPIv > > hardware acceleration is worse than software emulation? In addition, > > Actually this performance data was measured on the basis of fastpath > optimization while cpu runs at base frequency. > > As a result, IPI virtualization could have extra 15.98% cost reduction > over IPI fastpath process in x2apic mode. I observed that adaptive advance lapic timer and adaptive halt-polling will influence kvm-unit-tests/vmexit.flat IPI testing score, could you post the score after disabling these features as commit a9ab13ff6e (KVM: X86: Improve latency for single target IPI fastpath) mentioned？ In addition, please post the hackbench(./hackbench -l 1000000) and ipi microbenchmark scores. Wanpeng
