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Subject: Re: [PATCH v1 1/3] KVM: VMX: Consider PID.PIR to determine if vCPU
 has pending interrupts
To:     Joao Martins <joao.m.martins@oracle.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Liran Alon <liran.alon@oracle.com>,
        Jag Raman <jag.raman@oracle.com>
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 <030dd147-8c4f-d6e3-85a8-ee743ce4d5b0@oracle.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
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Date:   Mon, 11 Nov 2019 16:58:33 +0100
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On 11/11/19 15:59, Joao Martins wrote:
>> Should we check the bitmap only if SN is false?
                                            ^^^^^

Of course it should be skipped if SN is false, as you correctly say below.

>> We have a precondition
>> that if SN is clear then non-empty PIR implies ON=3D1 (modulo the small
>> window in vmx_vcpu_pi_load of course), so that'd be a bit faster.
> Makes sense;
>=20
> The bitmap check was really meant for SN=3D1.
>=20
> Should SN=3D0 we would be saving ~22-27 cycles as far as I micro-benchmar=
ked a few
> weeks ago. Now that you suggest it, it would be also good for older platf=
orms too.

Or even newer platforms if they don't use VT-d.

Paolo