linux-kernel - RE: [PATCH] x86/hyper-v: implement EOI assist

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Date:   Tue, 16 Apr 2019 00:21:10 +0000
From:   Long Li <longli@...rosoft.com>
To:     vkuznets <vkuznets@...hat.com>, Simon Xiao <sixiao@...rosoft.com>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>
Subject: RE: [PATCH] x86/hyper-v: implement EOI assist

>>>Subject: Re: [PATCH] x86/hyper-v: implement EOI assist
>>>
>>>Vitaly Kuznetsov <vkuznets@...hat.com> writes:
>>>
>>>> Hyper-V TLFS suggests an optimization to avoid imminent VMExit on EOI:
>>>> "The OS performs an EOI by atomically writing zero to the EOI Assist
>>>> field of the virtual VP assist page and checking whether the "No EOI
>>>required"
>>>> field was previously zero. If it was, the OS must write to the
>>>> HV_X64_APIC_EOI MSR thereby triggering an intercept into the
>>>hypervisor."
>>>>
>>>> Implement the optimization in Linux.
>>>>
>>>
>>>Simon, Long,
>>>
>>>did you get a chance to run some tests with this?

I have ran some tests on Azure L80s_v2.

With 10 NVMe disks on raid0 and formatted to EXT4, I'm getting 2.6m max IOPS with the patch, compared to 2.55m IOPS before.

The VM has been running stable. Thank you!

Tested-by: Long Li <longli@...rosoft.com>

>>>
>>>--
>>>Vitaly