Date: Wed, 16 Sep 2020 06:52:42 +0000 From: Wei Hu <weh@microsoft.com> To: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: MSR accesses that slows down the hypervisor/host Message-ID: <SG2P153MB0352138F1A840E8663C039C2BB210@SG2P153MB0352.APCP153.PROD.OUTLOOK.COM>
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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
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