linux-kernel - Re: [PATCH v2 06/10] x86/mce: Convert multiple if () statements into a switch() statement

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Message-ID: <c9ffb6b0-9c75-4990-afb5-33094d049570@intel.com>
Date: Mon, 21 Oct 2024 09:31:32 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: "Luck, Tony" <tony.luck@...el.com>, "Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>,
 "Mehta, Sohil" <sohil.mehta@...el.com>
Cc: "bp@...en8.de" <bp@...en8.de>, "tglx@...utronix.de" <tglx@...utronix.de>,
 "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
 "mingo@...hat.com" <mingo@...hat.com>, "hpa@...or.com" <hpa@...or.com>,
 "x86@...nel.org" <x86@...nel.org>,
 "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 06/10] x86/mce: Convert multiple if () statements into
 a switch() statement

On 10/21/24 09:06, Luck, Tony wrote:
>>         /*
>>          * All newer Intel systems support MCE broadcasting. Enable
>>          * synchronization with a one second timeout.
>>          */
>> -       if ((c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xe)) &&
>> -           cfg->monarch_timeout < 0)
>> +       if (c->x86_vfm >= INTEL_CORE_YONAH && cfg->monarch_timeout < 0)
>>                 cfg->monarch_timeout = USEC_PER_SEC;
> This change is correct. But the old code makes it more explicit that
> CPUs in families > 6 take this action. As the author of the VFM changes
> it's clear to me, maybe less so to others?
> 
> But maybe its OK.  The comment does help a lot. Anyone else have thoughts on this?

It certainly is a bit subtle.

To me, the earlier check would be even better if it were:

-	if (c->x86 < 6)
+	if (c->x86_vfm < INTEL_PENTIUM_PRO)
		return;

That at least makes it more clear that it's a range of models and avoids
having a ->x86 check mixed with a ->x86_vfm one.