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

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Message-ID: <Zq1wkyTkWCrdYx2-@liuwe-devbox-debian-v2>
Date: Fri, 2 Aug 2024 23:49:39 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Roman Kisel <romank@...ux.microsoft.com>
Cc: mhklinux@...look.com, kys@...rosoft.com, haiyangz@...rosoft.com,
	wei.liu@...nel.org, decui@...rosoft.com, tglx@...utronix.de,
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
	x86@...nel.org, hpa@...or.com, linux-hyperv@...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

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!