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Wed, 16 Sep 2020 06:52:43 +0000 From: Wei Hu To: "freebsd-hackers@freebsd.org" Subject: MSR accesses that slows down the hypervisor/host Thread-Topic: MSR accesses that slows down the hypervisor/host Thread-Index: AdaL9HYbtJyLPxf3TL+CSKzmJaxdTw== Date: Wed, 16 Sep 2020 06:52:42 +0000 Message-ID: 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: 71dba7f1-3113-42b6-6082-08d85a0d1c7d x-ms-traffictypediagnostic: SG2P15301MB0015: 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: WHIv/GCak8gHNMSxqxQgfcDpeYNnL4H45D0PuDiWag15YxTMZEv2wwMWKAIU+06Prw097mI0kYtvTuNVEiFmC4p7e+tMpI2YWo0bcliXzuPxqNxEhXgT6Fi++ZKxfyLbq5XbeOJZ81iGECI2Nz9agqkqPScvAcPYh7qhvm9zVmrzxjWleE8ip9r2yndyhD1ZgoAbLrle5vmCJNekoxmho+cKIoZbWG6e67EP1AdcPxAJPNvaBCZLpbpbOYtMe7FIk1DL6kHiHrKUk0wxJpvYq8RvJsmKml1WZsFkrLG6jHmYIaGQ0TBSDovJiUdZFk5pc06qZTC4KCJshVMkOcfT2O3lxTHGjDyERuQ0k44MSPolwUalNJYvqsO2bnjiV8CL x-forefront-antispam-report: CIP:255.255.255.255; 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TO_MATCH_ENVRCPT_ALL(0.00)[]; R_SPF_ALLOW(-0.20)[+ip4:40.107.0.0/16]; MIME_GOOD(-0.10)[text/plain]; NEURAL_HAM_LONG(-1.00)[-1.005]; RCPT_COUNT_ONE(0.00)[1]; RCVD_COUNT_THREE(0.00)[3]; WHITELIST_SPF_DKIM(-3.00)[microsoft.com:d:+,microsoft.com:s:+]; DKIM_TRACE(0.00)[microsoft.com:+]; DMARC_POLICY_ALLOW(-0.50)[microsoft.com,reject]; RCVD_IN_DNSWL_LOW(-0.10)[40.107.132.105:from]; TO_DN_EQ_ADDR_ALL(0.00)[]; NEURAL_HAM_SHORT(-0.83)[-0.830]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_LAST(0.00)[]; ASN(0.00)[asn:8075, ipnet:40.104.0.0/14, country:US]; ARC_ALLOW(-1.00)[microsoft.com:s=arcselector9901:i=1]; MAILMAN_DEST(0.00)[freebsd-hackers]; RWL_MAILSPIKE_POSSIBLE(0.00)[40.107.132.105:from] X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.33 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 16 Sep 2020 06:52:48 -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