linux-kernel - RE: [PATCH 1/1] x86/hyperv: Set X86_FEATURE_TSC_KNOWN

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Message-ID:
 <SN6PR02MB4157E061956EF4D394E587D8D4BF2@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Tue, 6 Aug 2024 02:01:55 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Wei Liu <wei.liu@...nel.org>, Roman Kisel <romank@...ux.microsoft.com>
CC: "kys@...rosoft.com" <kys@...rosoft.com>, "haiyangz@...rosoft.com"
	<haiyangz@...rosoft.com>, "decui@...rosoft.com" <decui@...rosoft.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>, "mingo@...hat.com"
	<mingo@...hat.com>, "bp@...en8.de" <bp@...en8.de>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, "x86@...nel.org"
	<x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
	"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/1] x86/hyperv: Set X86_FEATURE_TSC_KNOWN_FREQ when
 Hyper-V provides frequency

From: Wei Liu <wei.liu@...nel.org> Sent: Friday, August 2, 2024 4:50 PM
> 
> On Tue, Jun 11, 2024 at 07:51:48AM -0700, Roman Kisel wrote:
> >
> >
> > On 6/5/2024 7:55 PM, mhkelley58@...il.com wrote:
> > > From: Michael Kelley <mhklinux@...look.com>
> > >
> > > A Linux guest on Hyper-V gets the TSC frequency from a synthetic MSR, if
> > > available. In this case, set X86_FEATURE_TSC_KNOWN_FREQ so that Linux
> > > doesn't unnecessarily do refined TSC calibration when setting up the TSC
> > > clocksource.
> > >
> > > With this change, a message such as this is no longer output during boot
> > > when the TSC is used as the clocksource:
> > >
> > > [    1.115141] tsc: Refined TSC clocksource calibration: 2918.408 MHz
> > >
> > > Furthermore, the guest and host will have exactly the same view of the
> > > TSC frequency, which is important for features such as the TSC deadline
> > > timer that are emulated by the Hyper-V host.
> > >
> > > Signed-off-by: Michael Kelley <mhklinux@...look.com>
> > > ---
> > >   arch/x86/kernel/cpu/mshyperv.c | 1 +
> > >   1 file changed, 1 insertion(+)
> > >
> > > diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> > > index e0fd57a8ba84..c3e38eaf6d2f 100644
> > > --- a/arch/x86/kernel/cpu/mshyperv.c
> > > +++ b/arch/x86/kernel/cpu/mshyperv.c
> > > @@ -424,6 +424,7 @@ static void __init ms_hyperv_init_platform(void)
> > >   	    ms_hyperv.misc_features & HV_FEATURE_FREQUENCY_MSRS_AVAILABLE) {
> > >   		x86_platform.calibrate_tsc = hv_get_tsc_khz;
> > >   		x86_platform.calibrate_cpu = hv_get_tsc_khz;
> > > +		setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
> > >   	}
> > >   	if (ms_hyperv.priv_high & HV_ISOLATION) {
> >
> > LGTM
> >
> > Reviewed-by: Roman Kisel <romank@...ux.microsoft.com>
> 
> Applied to hyperv-fixes. Thanks!

Wei --

hyperv-fixes isn't showing this patch, or any of the others that your
emails said you applied last Friday.  Hence the patches aren't in
linux-next either.  Did something go awry?

Michael