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From: Zeng Guang <guang.zeng@intel.com>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm <kvm@vger.kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Tony Luck <tony.luck@intel.com>,
	Kan Liang <kan.liang@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Kim Phillips <kim.phillips@amd.com>,
	Jarkko Sakkinen <jarkko@kernel.org>,
	Jethro Beekman <jethro@fortanix.com>,
	Kai Huang <kai.huang@intel.com>,
	the arch/x86 maintainers <x86@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Robert Hu <robert.hu@intel.com>, Gao Chao <chao.gao@intel.com>
Subject: Re: [PATCH 0/5] IPI virtualization support for VM
Date: Sat, 17 Jul 2021 09:46:18 +0800	[thread overview]
Message-ID: <013e7d47-f3d6-4616-b1dc-1adc01b4058a@intel.com> (raw)
In-Reply-To: <CANRm+Cy=ncU-H7duei5q+CG+pm-kXvG8N8CiUQavQ3OEpDj9eg@mail.gmail.com>

On 7/16/2021 5:25 PM, Wanpeng Li wrote:
> On Fri, 16 Jul 2021 at 15:14, 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
>> 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,
> please post the IPI microbenchmark score w/ and w/o the
> patchset.(https://lore.kernel.org/kvm/20171219085010.4081-1-ynorov@caviumnetworks.com),
> I found that the hardware acceleration is not always outstanding.
> https://lore.kernel.org/kvm/CANRm+Cx597FNRUCyVz1D=B6Vs2GX3Sw57X7Muk+yMpi_hb+v1w@mail.gmail.com
We will check on it and get back later.  Thanks for your point.
>      Wanpeng

  reply	other threads:[~2021-07-17  1:46 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-16  6:48 [PATCH 0/5] IPI virtualization support for VM Zeng Guang
2021-07-16  6:48 ` [PATCH 1/6] x86/feat_ctl: Add new VMX feature, Tertiary VM-Execution control Zeng Guang
2021-07-28 23:44   ` Sean Christopherson
2021-07-29 15:56     ` Paolo Bonzini
2021-08-02  8:22     ` Zeng Guang
2021-08-02 16:20       ` Sean Christopherson
2021-07-16  6:48 ` [PATCH 2/6] KVM: VMX: Extend BUILD_CONTROLS_SHADOW macro to support 64-bit variation Zeng Guang
2021-07-16  6:48 ` [PATCH 3/6] KVM: VMX: Detect Tertiary VM-Execution control when setup VMCS config Zeng Guang
2021-07-29  0:03   ` Sean Christopherson
2021-08-02  6:59     ` Zeng Guang
2021-07-16  6:48 ` [PATCH 4/6] KVM: VMX: dump_vmcs() reports tertiary_exec_control field as well Zeng Guang
2021-07-16  6:48 ` [PATCH 5/6] KVM: x86: Support interrupt dispatch in x2APIC mode with APIC-write VM exit Zeng Guang
2021-07-16  6:48 ` [PATCH 6/6] KVM: VMX: enable IPI virtualization Zeng Guang
2021-07-16  9:52   ` Paolo Bonzini
2021-07-17  3:55     ` Zeng Guang
2021-07-18 20:32       ` Paolo Bonzini
2021-07-19 12:38         ` Zeng Guang
2021-07-19 13:58           ` Paolo Bonzini
2021-07-20  1:07             ` Zeng Guang
2021-07-19 13:16         ` Zeng Guang
2021-07-16  9:25 ` [PATCH 0/5] IPI virtualization support for VM Wanpeng Li
2021-07-17  1:46   ` Zeng Guang [this message]
2021-07-19  7:26   ` Zeng Guang
2021-07-19  7:37     ` Wanpeng Li
2021-07-23  6:15       ` Zeng Guang

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