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From:   Wanpeng Li <kernellwp@gmail.com>
Date:   Wed, 27 Jun 2018 08:49:08 +0800
Message-ID: <CANRm+CwNfOkosECeSGaXXDaqTDvh1u228ztU8C5Xe95FGgNsFQ@mail.gmail.com>
Subject: Re: [PATCH 0/4] x86/hyper-v: optimize PV IPIs
To:     Vitaly Kuznetsov <vkuznets@redhat.com>
Cc:     "the arch/x86 maintainers" <x86@kernel.org>,
        devel@linuxdriverproject.org, LKML <linux-kernel@vger.kernel.org>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Tianyu.Lan@microsoft.com,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@microsoft.com>
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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 can post one variant for Linux guest PV IPI if it also makes sense. :)

Regards,
Wanpeng Li