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Thu, 13 Nov 2025 22:19:38 -0800 Received: from satlexmb08.amd.com (10.181.42.217) by satlexmb10.amd.com (10.181.42.219) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.17; Thu, 13 Nov 2025 22:19:38 -0800 Received: from [10.252.219.240] (10.180.168.240) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server id 15.2.2562.17 via Frontend Transport; Thu, 13 Nov 2025 22:19:31 -0800 Message-ID: <780ec006-ca77-40bc-ae9e-8ed0ec093dc5@amd.com> Date: Fri, 14 Nov 2025 11:49:30 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 44/44] KVM: x86/pmu: Elide WRMSRs when loading guest PMCs if values already match To: Sean Christopherson , Marc Zyngier , Oliver Upton , Tianrui Zhao , Bibo Mao , Huacai Chen , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Xin Li , "H. 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X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On 8/7/2025 1:27 AM, Sean Christopherson wrote: > When loading a mediated PMU state, elide the WRMSRs to load PMCs with the > guest's value if the value in hardware already matches the guest's value. > For the relatively common case where neither the guest nor the host is > actively using the PMU, i.e. when all/many counters are '0', eliding the > WRMSRs reduces the latency of handling VM-Exit by a measurable amount > (WRMSR is significantly more expensive than RDPMC). > > As measured by KVM-Unit-Tests' CPUID VM-Exit testcase, this provides a > a ~25% reduction in latency (4k => 3k cycles) on Intel Emerald Rapids, > and a ~13% reduction (6.2k => 5.3k cycles) on AMD Turing. Nit. s/AMD Turing/AMD Turin -Manali > > Signed-off-by: Sean Christopherson _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv