linux-kernel - Re: [PATCH v2] x86/acrn: Set X86_FEATURE_TSC_KNOWN

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Date:   Mon, 14 Nov 2022 16:14:25 +0800
From:   Fei Li <fei1.li@...el.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        <peterz@...radead.org>, <dave.hansen@...el.com>,
        <gregkh@...uxfoundation.org>, <tglx@...utronix.de>,
        <mingo@...hat.com>, <dave.hansen@...ux.intel.com>, <hpa@...or.com>,
        <Yu1.Wang@...el.com>, <conghui.chen@...el.com>,
        <fengwei.yin@...el.com>, <junjie.mao@...el.com>
Subject: Re: [PATCH v2] x86/acrn: Set X86_FEATURE_TSC_KNOWN_FREQ

On 2022-11-07 at 16:30:27 +0100, Borislav Petkov wrote:
> On Tue, Nov 01, 2022 at 01:30:19PM +0800, Fei Li wrote:
> > If the TSC frequency is known from the acrn_get_tsc_khz(),
> > the TSC frequency does not need to be recalibrated.
Hi Borislav

Thanks for your comments. So sorry to reply you late.

> 
> What if the HV has unstable TSCs? How do you handle that?
> 
ACRN hypervisor assumes:
a) The TSC runs at a constant rate in all ACPI P-, C-. and T-states (i.e. invariant TSC)
b) The invariant TSC is based on only one invariant timekeeping hardware (called
   Always Running Timer or ART). ACRN main target uses for IoT devices
   which are typically one-socket
c) ACRN lives with temperature influence on TSC frequency

> > Avoiding recalibration by setting X86_FEATURE_TSC_KNOWN_FREQ.
> 
> Pls read section "2) Describe your changes" in
> Documentation/process/submitting-patches.rst for more details on how to
> write your commit message.
OK, will refine the commit message in v3. Thanks.
> 
> > This patch also removes `inline` for acrn_get_tsc_khz() since
> > it doesn't make sense.
> 
> Avoid having "This patch" or "This commit" in the commit message. It is
> tautologically useless.
> 
> Also, do
> 
> $ git grep 'This patch' Documentation/process
> 
> for more details.
OK. Thanks.
> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette