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([2001:b07:6468:f312:8c9d:1a6f:4730:367c]) by smtp.gmail.com with ESMTPSA id n23sm960755wmc.18.2019.11.11.13.59.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 Nov 2019 13:59:14 -0800 (PST) Subject: Re: [PATCH 1/2] KVM: X86: Single target IPI fastpath To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel References: <1573283135-5502-1-git-send-email-wanpengli@tencent.com> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: <4418c734-68e1-edaf-c939-f24d041acf2e@redhat.com> Date: Mon, 11 Nov 2019 22:59:14 +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: <1573283135-5502-1-git-send-email-wanpengli@tencent.com> Content-Language: en-US X-MC-Unique: kaTE4whwPeebLX5Z03K9mw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/11/19 08:05, Wanpeng Li wrote: > From: Wanpeng Li >=20 > This patch tries to optimize x2apic physical destination mode, fixed deli= very > mode single target IPI by delivering IPI to receiver immediately after se= nder > writes ICR vmexit to avoid various checks when possible. >=20 > Testing on Xeon Skylake server: >=20 > The virtual IPI latency from sender send to receiver receive reduces more= than > 330+ cpu cycles. >=20 > Running hackbench(reschedule ipi) in the guest, the avg handle time of MS= R_WRITE > caused vmexit reduces more than 1000+ cpu cycles: >=20 > Before patch: >=20 > VM-EXIT Samples Samples% Time% Min Time Max Time Avg ti= me > MSR_WRITE 5417390 90.01% 16.31% 0.69us 159.60us 1.08u= s >=20 > After patch: >=20 > VM-EXIT Samples Samples% Time% Min Time Max Time Avg ti= me > MSR_WRITE 6726109 90.73% 62.18% 0.48us 191.27us 0.58u= s Do you have retpolines enabled? The bulk of the speedup might come just from the indirect jump. Paolo