linux-kernel - Re: [PATCH v4] x86/cpu/intel: Fix the constant

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Message-ID: <e72b9895-c143-4818-901b-7d8ab26b8e91@intel.com>
Date: Mon, 4 Aug 2025 13:37:00 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: Suchit Karunakaran <suchitkarunakaran@...il.com>
CC: <skhan@...uxfoundation.org>, <linux-kernel-mentees@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <hpa@...or.com>, <darwi@...utronix.de>,
	<peterz@...radead.org>, <ravi.bangoria@....com>
Subject: Re: [PATCH v4] x86/cpu/intel: Fix the constant_tsc model check for
 Pentium 4

Hi Suchit

I would strongly suggest spending more time understanding reviewer
feedback and incorporating it before sending another version. Most of
the comments below are a repeat from previous reviews by multiple folks.


On 8/4/2025 10:59 AM, Suchit Karunakaran wrote:
> Pentium 4's which are INTEL_P4_PRESCOTT (model 0x03) and later have
> a constant TSC. This was correctly captured until commit fadb6f569b10
> ("x86/cpu/intel: Limit the non-architectural constant_tsc model checks").
> In that commit, an error was introduced while selecting the last P4
> model (0x06) as the upper bound. Model 0x06 was transposed to
> INTEL_P4_WILLAMETTE, which is just plain wrong. That was presumably a
> simple typo, probably just copying and pasting the wrong P4 model.
> Fix the constant TSC logic to cover all later P4 models. End at
> INTEL_P4_CEDARMILL which accurately corresponds to the last P4 model.


Please use proper spacing and line breaks. Posting this as a single
chunk makes it very hard to read.

> Fixes: fadb6f569b10 ("x86/cpu/intel: Limit the non-architectural constant_tsc model checks")
> 
> Cc: <stable@...r.kernel.org> # v6.15
> 
> Signed-off-by: Suchit Karunakaran <suchitkarunakaran@...il.com>
> 

No blank lines between these 3 statements.

Please take all review comments seriously, even if they are nits.

https://lore.kernel.org/lkml/2025073013-stimulus-snowdrift-d28c@gregkh/

> Changes since v3:
> - Refined changelog
> 
> Changes since v2:
> - Improve commit message
> 
> Changes since v1:
> - Fix incorrect logic
> 

Patch-to-patch changes go below the --- line.

You have been provided the same feedback by other folks as well.

https://lore.kernel.org/lkml/61958a3cca40fc9a42b951c68c75f138cab9212e.camel@perches.com/

https://lore.kernel.org/lkml/2d30ee37-8069-4443-8a80-5233b3b23f66@intel.com/

If you are not sure, please look at other submissions to the mailing
list that do this.

> ---
>  arch/x86/kernel/cpu/intel.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index 076eaa41b8c8..6f5bd5dbc249 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -262,7 +262,7 @@ static void early_init_intel(struct cpuinfo_x86 *c)
>  	if (c->x86_power & (1 << 8)) {
>  		set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
>  		set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
> -	} else if ((c->x86_vfm >= INTEL_P4_PRESCOTT && c->x86_vfm <= INTEL_P4_WILLAMETTE) ||
> +	} else if ((c->x86_vfm >=  INTEL_P4_PRESCOTT && c->x86_vfm <= INTEL_P4_CEDARMILL) ||
>  		   (c->x86_vfm >= INTEL_CORE_YONAH  && c->x86_vfm <= INTEL_IVYBRIDGE)) {

Again, this changes the previous alignment. You do not need the extra
space before INTEL_P4_PRESCOTT. Avoiding that would keep both the lines
aligned.

https://lore.kernel.org/lkml/30f01900-e79f-4947-b0b4-c4ba29d18084@intel.com/

It's acceptable to ask clarifying questions, but disregarding review
comments frustrates reviewers and inclined to ignore future submissions.


>  		set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
>  	}