linux-kernel - Re: [PATCH v3 0/6] KVM: X86: Implement PV IPIs support

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Date:   Wed, 18 Jul 2018 11:00:39 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH v3 0/6] KVM: X86: Implement PV IPIs support

Gentle ping, hope this series can catch up with the next merge window. :)
On Tue, 3 Jul 2018 at 14:21, Wanpeng Li <kernellwp@...il.com> wrote:
>
> Using hypercall to send IPIs by one vmexit instead of one by one for
> xAPIC/x2APIC physical mode and one vmexit per-cluster for x2APIC cluster
> mode. Intel guest can enter x2apic cluster mode when interrupt remmaping
> is enabled in qemu, however, latest AMD EPYC still just supports xapic
> mode which can get great improvement by PV IPIs. This patchset supports
> PV IPIs for maximal 128 vCPUs VM, it is big enough for cloud environment
> currently, supporting more vCPUs needs to introduce more complex logic,
> in the future this might be extended if needed.
>
> Hardware: Xeon Skylake 2.5GHz, 2 sockets, 40 cores, 80 threads, the VM
> is 80 vCPUs, IPI microbenchmark(https://lkml.org/lkml/2017/12/19/141):
>
> x2apic cluster mode, vanilla
>
>  Dry-run:                         0,            2392199 ns
>  Self-IPI:                  6907514,           15027589 ns
>  Normal IPI:              223910476,          251301666 ns
>  Broadcast IPI:                   0,         9282161150 ns
>  Broadcast lock:                  0,         8812934104 ns
>
> x2apic cluster mode, pv-ipi
>
>  Dry-run:                         0,            2449341 ns
>  Self-IPI:                  6720360,           15028732 ns
>  Normal IPI:              228643307,          255708477 ns
>  Broadcast IPI:                   0,         7572293590 ns  => 22% performance boost
>  Broadcast lock:                  0,         8316124651 ns
>
> x2apic physical mode, vanilla
>
>  Dry-run:                         0,            3135933 ns
>  Self-IPI:                  8572670,           17901757 ns
>  Normal IPI:              226444334,          255421709 ns
>  Broadcast IPI:                   0,        19845070887 ns
>  Broadcast lock:                  0,        19827383656 ns
>
> x2apic physical mode, pv-ipi
>
>  Dry-run:                         0,            2446381 ns
>  Self-IPI:                  6788217,           15021056 ns
>  Normal IPI:              219454441,          249583458 ns
>  Broadcast IPI:                   0,         7806540019 ns  => 154% performance boost
>  Broadcast lock:                  0,         9143618799 ns
>
> v2 -> v3:
>  * rename ipi_mask_done to irq_restore_exit, __send_ipi_mask return int
>    instead of bool
>  * fix build errors reported by 0day
>  * split patches, nothing change
>
> v1 -> v2:
>  * sparse apic id > 128, or any other errors, fallback to original apic hooks
>  * have two bitmask arguments so that one hypercall handles 128 vCPUs
>  * fix KVM_FEATURE_PV_SEND_IPI doc
>  * document hypercall
>  * fix NMI selftest fails
>  * fix build errors reported by 0day
>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
>
> Wanpeng Li (6):
>   KVM: X86: Add kvm hypervisor init time platform setup callback
>   KVM: X86: Implement PV IPIs in linux guest
>   KVM: X86: Fallback to original apic hooks when bad happens
>   KVM: X86: Implement PV IPIs send hypercall
>   KVM: X86: Add NMI support to PV IPIs
>   KVM: X86: Expose PV_SEND_IPI CPUID feature bit to guest
>
>  Documentation/virtual/kvm/cpuid.txt      |   4 ++
>  Documentation/virtual/kvm/hypercalls.txt |   6 ++
>  arch/x86/include/uapi/asm/kvm_para.h     |   1 +
>  arch/x86/kernel/kvm.c                    | 101 +++++++++++++++++++++++++++++++
>  arch/x86/kvm/cpuid.c                     |   3 +-
>  arch/x86/kvm/x86.c                       |  42 +++++++++++++
>  include/uapi/linux/kvm_para.h            |   1 +
>  7 files changed, 157 insertions(+), 1 deletion(-)
>
> --
> 2.7.4
>