linux-kernel - Re: [PATCH RFC] x86/tsc: Make recalibration default on for TSC_KNOWN

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Message-ID: <20230522161158.GA3330346@hirez.programming.kicks-ass.net>
Date:   Mon, 22 May 2023 18:11:58 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...el.com>,
        "H . Peter Anvin" <hpa@...or.com>, paulmck@...nel.org,
        rui.zhang@...el.com, x86@...nel.org, linux-kernel@...r.kernel.org,
        bin.gao@...el.com
Subject: Re: [PATCH RFC] x86/tsc: Make recalibration default on for
 TSC_KNOWN_FREQ cases

On Mon, May 22, 2023 at 11:20:15PM +0800, Feng Tang wrote:

> And I don't understand the commit log: "On Intel GOLDMONT Atom SoC
> TSC is the only reliable clocksource. We mark TSC reliable to avoid
> watchdog on it."
> 
> Clearly the Denventon I found today has both HPET and ACPI_PM timer:
> 
>   [root@...0 ~]# grep .  /sys/devices/system/clocksource/clocksource0/*
>   /sys/devices/system/clocksource/clocksource0/available_clocksource:tsc hpet acpi_pm
>   /sys/devices/system/clocksource/clocksource0/current_clocksource:tsc
>   
> The lscpu info is:
>   
>   Architecture:                    x86_64
>   CPU op-mode(s):                  32-bit, 64-bit
>   Address sizes:                   39 bits physical, 48 bits virtual
>   Byte Order:                      Little Endian
>   CPU(s):                          12
>   On-line CPU(s) list:             0-11
>   Vendor ID:                       GenuineIntel
>   BIOS Vendor ID:                  Intel(R) Corporation
>   Model name:                      Intel(R) Atom(TM) CPU C3850 @ 2.10GHz
>   BIOS Model name:                 Intel(R) Atom(TM) CPU C3850 @ 2.10GHz  CPU @ 2.1GHz
>   BIOS CPU family:                 43
>   CPU family:                      6
>   Model:                           95
>   Thread(s) per core:              1
>   Core(s) per socket:              12
>   Socket(s):                       1
>   Stepping:                        1
> 
> Maybe this cpu model (0x5F) has been used by some type of platforms
> which has met the false alarm watchdog issue.

It has them; but they are not *reliable*.