linux-kernel - Re: [PATCH v2 02/17] x86/smpboot: Fix INIT delay optimization for extended Intel Families

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Message-ID: <b8941997-81c1-490c-8f23-62070f7a46a2@intel.com>
Date: Tue, 11 Feb 2025 12:20:02 -0800
From: Sohil Mehta <sohil.mehta@...el.com>
To: Dave Hansen <dave.hansen@...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>, Jean Delvare <jdelvare@...e.com>, Guenter Roeck
	<linux@...ck-us.net>, Zhang Rui <rui.zhang@...el.com>, Andrew Cooper
	<andrew.cooper3@...rix.com>, "David Laight" <david.laight.linux@...il.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: [PATCH v2 02/17] x86/smpboot: Fix INIT delay optimization for
 extended Intel Families

On 2/11/2025 12:10 PM, Dave Hansen wrote:
> On 2/11/25 11:43, Sohil Mehta wrote:
>> Currently only Family 6 is considered as modern and avoids the 10 msec
>> INIT delay. The optimization doesn't extend to the upcoming Family 18/19
>> models.
> 
> This doesn't quite parse correctly to me.
> 
> Let's say it this way:
> 
> 	Some old crusty CPUs need an extra delay that slows down
> 	booting. See the comment above 'init_udelay' for details. Newer
> 	CPUs don't need the delay.
> 
> 	Right now, for Intel, Family 6 and only Family 6 skips the
> 	delay. That leaves out both the Family 15 (Pentium 4s) and brand
> 	new Family 18/19 models.
> 
> 	The omission of Family 15 (Pentium 4s) seems like an oversight
> 	and 18/19 do not need the delay.
> 
> 	Skip the delay on all Intel processors Family 6 and beyond.
> 
> Is there anything wrong there?

No, it is accurate.