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Wed, 16 Sep 2020 07:00:59 +0000 From: Wei Hu To: "freebsd-virtualization@freebsd.org" Subject: MSR accesses that slows down the hypervisor/host Thread-Topic: MSR accesses that slows down the hypervisor/host Thread-Index: AdaL9HYbtJyLPxf3TL+CSKzmJaxdTwAApTvQ Date: Wed, 16 Sep 2020 07:00:58 +0000 Message-ID: References: In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [167.220.255.32] x-ms-publictraffictype: Email x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 3946e74f-8079-4f21-41b1-08d85a0e4416 x-ms-traffictypediagnostic: SG2P15301MB0062: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:9508; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: KB810QaTzuFwAHBPesxFLACm3CYCc024fpGiyWL1VvT6ZUofZLT5HoIUB2Y7cBqOHf1IFoAnjSr4mpjdWG1LyyP2RNYQmAMHRNIepXqBwb+mJQJM/OhwbYyviBCN41kuTZUSNsKlK4tRCk0josfi/Zl0ZuDh5mGta9/lnDv6Diped5N2IVhR3j4JloqB0+wuGNDrtAvb5BBALhSw5ws2ZYVbYeXyi5Kpyj6jULQn5D2aKs207M5ZXmhyv9xKBt7O0UW2rfU4cTYySgIRrAh96m6C8sCdKcEL1XWtLbzYSJ/SpVDbOYCvvoWBYUueNxNYsU/dY6uda5hxli+q2YeuEtLuPxnuww27WpnghxRjkG/MDK56RcIxHrx3mPvweyDD x-forefront-antispam-report: CIP:255.255.255.255; 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List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 16 Sep 2020 07:01:07 -0000 Hello, There are couple AMD processor related MSRs which are being accessed in Fre= eBSD.=20 #define MSR_AMDK8_IPM 0xc0010055 #define MSR_LS_CFG 0xc0011020 We are seeing a lot of CPU time being spent in the host (Hyper-V) in handli= ng traps when accessing these MSRs. Especially the first MRS is frequently = being accessed in cpu_idle() so the performance impact to host is significa= nt. We noted that Linux made some code changes in the 4.10 kernel to access the= first MSR much less frequently. So we are wondering if there are similar c= hanges in FreeBSD that might be in the plan. Microsoft Hyper-V team is also= planning some work to speed up the accesses to these MSRs. However any sug= gestions or plan to improve in the FreeBSD guest are welcome. Thanks, Wei