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    SubjectRe: [PATCH 0/4] x86/hyper-v: optimize PV IPIs
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    Wanpeng Li <kernellwp@gmail.com> writes:

    > Hi Vitaly, (fix my reply mess this time)
    > On Sat, 23 Jun 2018 at 01:09, Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
    >>
    >> When reviewing my "x86/hyper-v: use cheaper HVCALL_FLUSH_VIRTUAL_ADDRESS_
    >> {LIST,SPACE} hypercalls when possible" patch Michael suggested to apply the
    >> same idea to PV IPIs. Here we go!
    >>
    >> Despite what Hyper-V TLFS says about HVCALL_SEND_IPI hypercall, it can
    >> actually be 'fast' (passing parameters through registers). Use that too.
    >>
    >> This series can collide with my "KVM: x86: hyperv: PV IPI support for
    >> Windows guests" series as I rename ipi_arg_non_ex/ipi_arg_ex structures
    >> there. Depending on which one gets in first we may need to do tiny
    >> adjustments.
    >
    > As hyperv PV TLB flush has already been merged, is there any other
    > obvious multicast IPIs scenarios? qemu supports interrupt remapping
    > since two years ago, I think windows guest can switch to cluster mode
    > after entering x2APIC, so sending IPI per cluster. In addition, you
    > can also post the benchmark result for this PV IPI optimization,
    > although it also fixes the bug which you mentioned above.

    I got confused, which of my patch series are you actually looking at?
    :-)

    This particular one ("x86/hyper-v: optimize PV IPIs") is not about
    KVM/qemu, it is for Linux running on top on real Hyper-V server. We
    already support PV IPIs and here I'm just trying to optimize the way how
    we send them by switching to a cheaper hypercall (and using 'fast'
    version of it) when possible. I don't actually have a good benchmark
    (and I don't remember seeing one when K.Y. posted PV IPI support) but
    this can be arranged I guess: I can write a dump 'IPI sender' in kernel
    and send e.g. 1000 IPIs.

    --
    Vitaly

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