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([2001:b07:6468:f312:a0f7:472a:1e7:7ef]) by smtp.gmail.com with ESMTPSA id w17sm8727264wrt.45.2019.11.11.07.58.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 Nov 2019 07:58:31 -0800 (PST) Subject: Re: [PATCH v1 1/3] KVM: VMX: Consider PID.PIR to determine if vCPU has pending interrupts To: Joao Martins Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Liran Alon , Jag Raman References: <20191106175602.4515-1-joao.m.martins@oracle.com> <20191106175602.4515-2-joao.m.martins@oracle.com> <67bca655-fea3-4b57-be3c-7dc58026b5d9@redhat.com> <030dd147-8c4f-d6e3-85a8-ee743ce4d5b0@oracle.com> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: <5ee4c4ae-9d22-d560-bb61-e5f40b56da2e@redhat.com> Date: Mon, 11 Nov 2019 16:58:33 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <030dd147-8c4f-d6e3-85a8-ee743ce4d5b0@oracle.com> Content-Language: en-US X-MC-Unique: XkxVwxuFPNyTCVhildMu6g-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org 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