Date: Sun, 20 Sep 2020 07:41:12 +0000 From: Wei Hu <weh@microsoft.com> To: Konstantin Belousov <kostikbel@gmail.com>, "avg@freebsd.org" <avg@freebsd.org> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: RE: MSR accesses that slows down the hypervisor/host Message-ID: <SG2P153MB03521E6C5A0870A42097E8C8BB3D0@SG2P153MB0352.APCP153.PROD.OUTLOOK.COM> In-Reply-To: <20200917183825.GU94807@kib.kiev.ua> References: <SG2P153MB0352138F1A840E8663C039C2BB210@SG2P153MB0352.APCP153.PROD.OUTLOOK.COM> <20200916135727.GO94807@kib.kiev.ua> <SG2P153MB0352C010CAA61A46BD28C964BB3E0@SG2P153MB0352.APCP153.PROD.OUTLOOK.COM> <20200917183825.GU94807@kib.kiev.ua>
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> > > From: Konstantin Belousov <kostikbel@gmail.com> > > > Sent: Wednesday, September 16, 2020 9:57 PM > > > To: Wei Hu <weh@microsoft.com> > > > Cc: freebsd-hackers@freebsd.org > > > Subject: Re: MSR accesses that slows down the hypervisor/host > > > > > > Where do you see accesses to MSR_LS_CFG ? I can only find > > > manipulations of that MSR in init_amd(), and then it is all under > > > check that we are not virtualized. > > > > > Yes, it is only accessed in init_amd() at boot time. So it is less > > concerned. MSR_AMDK8_IPM is accessed in cpu_idle() all the time, so it = is > the key place to optimize. > > > > > For MSR_AMDK8_IPM access in cpu_idle(), it seems that the workaround > > > was applied too wide. It might be that we do not need to do it on > > > recent CPUs, but I need to spent more time looking at datasheets to > confirm/deny. > > > > > > But, do you (hypervisor) indeed allow guest to initiate C1 or deeper = idle > state ? > > > If not, perhaps as the first measure, we can avoid manipulating > > > MSR_AMDK8_IPM under hypervisor at all. > > > > You are right a guest cannot initiate C1 or deeper idle state when runn= ing on > Hyper-V. > > So skipping the read of MSR_AMDK8_IPM when running under this > > hypervisor would Be a viable solution. >=20 > https://nam06.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Frevie= ws > .freebsd.org%2FD26470&data=3D02%7C01%7Cweh%40microsoft.com%7C8 > 7f5f82583ee428f49c108d85b38e9c3%7C72f988bf86f141af91ab2d7cd011db4 > 7%7C1%7C0%7C637359647283571535&sdata=3DJdKxHO1sM2InD7Eo793FF > RIpj5AQmowcc%2BLGW19dlH4%3D&reserved=3D0 Thanks for the quick response. I will review the change and do some tests o= n Hyper-V. Wei
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