linux-kernel - Re: [PATCH RESEND] x86/tsc: print some log if calibrated tsc freq deviates from original too much

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Date: Tue, 9 Apr 2024 10:05:46 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Lei Chen <lei.chen@...rtx.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND] x86/tsc: print some log if calibrated tsc freq
 deviates from original too much


* Lei Chen <lei.chen@...rtx.com> wrote:

> In most cases, tsc_khz is refined by hpet on boot. But in a few
> production-level nodes, the refinement fails because calibrated
> freq diviates from origin tsc freq more than 1%. Printing some
> logs will help get this info.
> 
> Signed-off-by: Lei Chen <lei.chen@...rtx.com>
> ---
>  arch/x86/kernel/tsc.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 15f97c0abc9d..a68b16e72df1 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -1435,8 +1435,15 @@ static void tsc_refine_calibration_work(struct work_struct *work)
>  	}
>  
>  	/* Make sure we're within 1% */
> -	if (abs(tsc_khz - freq) > tsc_khz/100)
> +	if (abs(tsc_khz - freq) > tsc_khz/100) {
> +		pr_warn("Warning: TSC freq calibrated by [%s]: %lu.%03lu MHz deviates too much from original freq: %lu.%03lu MHz\n",

Yeah, so it wouldn't cost us anything to more precisely define 'too much':

 s/deviates too much from
  /deviates by more than 1% from

Right?

> +			hpet ? "HPET" : "PM_TIMER",
> +			(unsigned long)freq / 1000,
> +			(unsigned long)freq % 1000,
> +			(unsigned long)tsc_khz / 1000,
> +			(unsigned long)tsc_khz % 1000);
>  		goto out;
> +	}

The warning makes sense I suppose, if it's one per system and once per 
bootup [right?], but I think pr_info() would be plenty enough priority for 
this condition - especially as we didn't have the warning before and don't 
know how frequent it is?

Thanks,

	Ingo