Messages in this thread | | | Subject | Re: Re: Re: [PATCH] x86/kvm: Introduce boot parameter no-kvm-pvipi | From | zhenwei pi <> | Date | Thu, 21 Oct 2021 15:17:21 +0800 |
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On 10/21/21 1:03 PM, Wanpeng Li wrote: > On Thu, 21 Oct 2021 at 11:05, zhenwei pi <pizhenwei@bytedance.com> wrote: >> >> >> On 10/21/21 4:12 AM, Sean Christopherson wrote: >>> On Wed, Oct 20, 2021, Wanpeng Li wrote: >>>> On Wed, 20 Oct 2021 at 20:08, zhenwei pi <pizhenwei@bytedance.com> wrote: >>>>> >>>>> Although host side exposes KVM PV SEND IPI feature to guest side, >>>>> guest should still have a chance to disable it. >>>>> >>>>> A typicall case of this parameter: >>>>> If the host AMD server enables AVIC feature, the flat mode of APIC >>>>> get better performance in the guest. >>>> >>>> Hmm, I didn't find enough valuable information in your posting. We >>>> observe AMD a lot before. >>>> https://lore.kernel.org/all/CANRm+Cx597FNRUCyVz1D=B6Vs2GX3Sw57X7Muk+yMpi_hb+v1w@mail.gmail.com/T/#u >>> >>> I too would like to see numbers. I suspect the answer is going to be that >>> AVIC performs poorly in CPU overcommit scenarios because of the cost of managing >>> the tables and handling "failed delivery" exits, but that AVIC does quite well >>> when vCPUs are pinned 1:1 and IPIs rarely require an exit to the host. >>> >> >> Test env: >> CPU: AMD EPYC 7642 48-Core Processor >> >> Kmod args(enable avic and disable nested): >> modprobe kvm-amd nested=0 avic=1 npt=1 >> >> QEMU args(disable x2apic): >> ... -cpu host,x2apic=off ... >> >> Benchmark tool: >> https://github.com/bytedance/kvm-utils/tree/master/microbenchmark/apic-ipi >> >> ~# insmod apic_ipi.ko options=5 && dmesg -c >> >> apic_ipi: 1 NUMA node(s) >> apic_ipi: apic [flat] >> apic_ipi: apic->send_IPI[default_send_IPI_single+0x0/0x40] >> apic_ipi: apic->send_IPI_mask[kvm_send_ipi_mask+0x0/0x10] >> apic_ipi: IPI[kvm_send_ipi_mask] from CPU[0] to CPU[1] >> apic_ipi: total cycles 375671259, avg 3756 >> apic_ipi: IPI[flat_send_IPI_mask] from CPU[0] to CPU[1] >> apic_ipi: total cycles 221961822, avg 2219 >> >> >> apic->send_IPI_mask[kvm_send_ipi_mask+0x0/0x10] >> -> This line show current send_IPI_mask is kvm_send_ipi_mask(because >> of PV SEND IPI FEATURE) >> >> apic_ipi: IPI[kvm_send_ipi_mask] from CPU[0] to CPU[1] >> apic_ipi: total cycles 375671259, avg 3756 >> -->These lines show the average cycles of each kvm_send_ipi_mask: 3756 >> >> apic_ipi: IPI[flat_send_IPI_mask] from CPU[0] to CPU[1] >> apic_ipi: total cycles 221961822, avg 2219 >> -->These lines show the average cycles of each flat_send_IPI_mask: 2219 > > Just single target IPI is not eough. > > Wanpeng >
Benchmark smp_call_function_single (https://github.com/bytedance/kvm-utils/blob/master/microbenchmark/ipi-bench/ipi_bench.c):
Test env: CPU: AMD EPYC 7642 48-Core Processor
Kmod args(enable avic and disable nested): modprobe kvm-amd nested=0 avic=1 npt=1
QEMU args(disable x2apic): ... -cpu host,x2apic=off ...
1> without no-kvm-pvipi: ipi_bench_single wait[1], CPU0[NODE0] -> CPU1[NODE0], loop = 100000 elapsed = 424945631 cycles, average = 4249 cycles ipitime = 385246136 cycles, average = 3852 cycles ipi_bench_single wait[0], CPU0[NODE0] -> CPU1[NODE0], loop = 100000 elapsed = 419057953 cycles, average = 4190 cycles
2> with no-kvm-pvipi: ipi_bench_single wait[1], CPU0[NODE0] -> CPU1[NODE0], loop = 100000 elapsed = 321756407 cycles, average = 3217 cycles ipitime = 299433550 cycles, average = 2994 cycles ipi_bench_single wait[0], CPU0[NODE0] -> CPU1[NODE0], loop = 100000 elapsed = 295382146 cycles, average = 2953 cycles
-- zhenwei pi
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