linux-kernel - Re: [RFC PATCH 02/15] x86/apic: Fix smp init delay for extended Intel families

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Message-ID: <0875ab7b-0595-4195-924c-66da28074ef6@intel.com>
Date: Fri, 20 Dec 2024 15:20:35 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Sohil Mehta <sohil.mehta@...el.com>, x86@...nel.org,
 Dave Hansen <dave.hansen@...ux.intel.com>, Tony Luck <tony.luck@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>,
 Kan Liang <kan.liang@...ux.intel.com>, Thomas Gleixner <tglx@...utronix.de>,
 Borislav Petkov <bp@...en8.de>, "H . Peter Anvin" <hpa@...or.com>,
 "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Andy Lutomirski <luto@...nel.org>, Viresh Kumar <viresh.kumar@...aro.org>,
 Fenghua Yu <fenghua.yu@...el.com>, Jean Delvare <jdelvare@...e.com>,
 Guenter Roeck <linux@...ck-us.net>, Zhang Rui <rui.zhang@...el.com>,
 linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org,
 linux-hwmon@...r.kernel.org
Subject: Re: [RFC PATCH 02/15] x86/apic: Fix smp init delay for extended Intel
 families

On 12/20/24 13:36, Sohil Mehta wrote:
> The MP specification version 1.4 references the i486 and early Pentium
> processors in family 5. 

Can you please elaborate on how this reference is relevant to the patch
at hand?

> However, all processors starting with family 6 likely do not need the
> 10 msec INIT delay. The omission of the Pentium 4s (family 15) seems
> like an oversight in the original check.
> 
> With some risk, choose a simpler check and extend the quirk to all
> recent and upcoming Intel processors.

I'm struggling to follow this a bit.

I think these are the facts that matter:

 * init_udelay=0 means "no quirk"
 * Modern CPUs don't have the quirk
 * The current check says "only family 6 is modern"
 * Family 15 is _probably_ modern and just forgotten about

And this is what you're doing in the end:

Consider everything PPro and later to be modern, including all of
families 6, 15 and the new 18/19 CPUs.

Right?