linux-kernel - Re: [patch v5 06/19] x86/cpu: Provide a sane leaf 0xb/0x1f parser

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Date: Mon, 12 Feb 2024 16:08:31 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Borislav Petkov <bp@...en8.de>
Cc: LKML <linux-kernel@...r.kernel.org>, x86@...nel.org, Tom Lendacky
 <thomas.lendacky@....com>, Andrew Cooper <andrew.cooper3@...rix.com>,
 Arjan van de Ven <arjan@...ux.intel.com>, Huang Rui <ray.huang@....com>,
 Juergen Gross <jgross@...e.com>, Dimitri Sivanich
 <dimitri.sivanich@....com>, Sohil Mehta <sohil.mehta@...el.com>, K Prateek
 Nayak <kprateek.nayak@....com>, Kan Liang <kan.liang@...ux.intel.com>,
 Zhang Rui <rui.zhang@...el.com>, "Paul E. McKenney" <paulmck@...nel.org>,
 Feng Tang <feng.tang@...el.com>, Andy Shevchenko <andy@...radead.org>,
 Michael Kelley <mhklinux@...look.com>, "Peter Zijlstra (Intel)"
 <peterz@...radead.org>
Subject: Re: [patch v5 06/19] x86/cpu: Provide a sane leaf 0xb/0x1f parser

On Mon, Feb 12 2024 at 16:00, Borislav Petkov wrote:
> On Mon, Feb 12, 2024 at 03:17:45PM +0100, Thomas Gleixner wrote:
>> Especially x2apic_shift is horrible and the comments of EBX are visually
>> impaired while with the C++ comments x2apic_shift looks natural and the
>> EBX comments are just open to the right and therefore simpler.
>
> I'd say, put comments *above* the member versus on the side. We don't
> like side comments, if you remember. :-)

In code, no. For struct definitions if they are strictly tabular
formatted, they are actually nice as they are more compact and take less
space than the above member variant.

		// eax
		u32	x2apic_shift	:  5, // Number of bits to shift APIC ID right
					      // for the topology ID at the next level
					: 27; // Reserved
		// ebx
		u32	num_processors	: 16, // Number of processors at current level
					: 16; // Reserved

versus:

		/* eax */
                	/*
                         * Number of bits to shift APIC ID right for the topology ID
	                 * at the next level
                         */
		u32	x2apic_shift	:  5,
                	/* Reserved */
					: 27;

		/* ebx */
                	 /* Number of processors at current level */
		u32	num_processors	: 16,
                	 /* Reserved */
					: 16;

This really makes my eyes bleed.