From:   Kechen Lu <kechenl@nvidia.com>
To:     Zhi Wang <zhi.wang.linux@gmail.com>
CC:     "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "seanjc@google.com" <seanjc@google.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "chao.gao@intel.com" <chao.gao@intel.com>,
        "shaoqin.huang@intel.com" <shaoqin.huang@intel.com>,
        "vkuznets@redhat.com" <vkuznets@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [RFC PATCH v6 6/6] KVM: selftests: Add tests for VM and vCPU cap
 KVM_CAP_X86_DISABLE_EXITS
Thread-Topic: [RFC PATCH v6 6/6] KVM: selftests: Add tests for VM and vCPU cap
 KVM_CAP_X86_DISABLE_EXITS
Thread-Index: AQHZLT1DFK7gYbjBnUSEFj79Obk3Bq671fcAgABMnVA=
Date:   Thu, 2 Feb 2023 20:17:04 +0000
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References: <20230121020738.2973-1-kechenl@nvidia.com>
        <20230121020738.2973-7-kechenl@nvidia.com>
 <20230202170836.000078f1@gmail.com>
In-Reply-To: <20230202170836.000078f1@gmail.com>
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Hi Zhi,

> -----Original Message-----
> From: Zhi Wang <zhi.wang.linux@gmail.com>
> Sent: Thursday, February 2, 2023 7:09 AM
> To: Kechen Lu <kechenl@nvidia.com>
> Cc: kvm@vger.kernel.org; seanjc@google.com; pbonzini@redhat.com;
> chao.gao@intel.com; shaoqin.huang@intel.com; vkuznets@redhat.com;
> linux-kernel@vger.kernel.org
> Subject: Re: [RFC PATCH v6 6/6] KVM: selftests: Add tests for VM and vCPU
> cap KVM_CAP_X86_DISABLE_EXITS
>=20
> External email: Use caution opening links or attachments
>=20
>=20
> On Sat, 21 Jan 2023 02:07:38 +0000
> Kechen Lu <kechenl@nvidia.com> wrote:
>=20
> It works on my box now. LGTM. I was curious if there is any other userspa=
ce
> application using this? It would be interesting to see their strategies.
>=20
Thanks for testing this! Appreciated.=20

For userspace applications, we had a POC with the changes in QEMU, to do th=
e static per-vCPU HLT disabling, depending on the users to have the flexibi=
lity run guest workloads on these none-hlt-exits vCPUs instead of disabling=
 hlt exits for whole VM, we saw 3%+ performance benefits. Furthermore, we h=
ad the dynamically toggled hlt exits strategy applied on QEMU, which depend=
ing on the guest stats and heuristics to do the hlt exits toggling.

BR,
Kechen