linux-kernel - Re: [patch v5 09/19] x86/cpu: Provide an AMD/HYGON specific topology parser

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Date: Fri, 2 Feb 2024 13:30:11 +0100
From: Borislav Petkov <bp@...en8.de>
To: Thomas Gleixner <tglx@...utronix.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 09/19] x86/cpu: Provide an AMD/HYGON specific topology
 parser

On Tue, Jan 23, 2024 at 01:53:43PM +0100, Thomas Gleixner wrote:
> +static bool parse_8000_0008(struct topo_scan *tscan)
> +{
> +	struct {
> +		u32	ncores		:  8,

Yeah, so there was some confusion what this field actually means. It is
documented correctly in the latest APM:

"NT: number of physical threads - 1. The number of threads in the
processor is NT+1 (e.g., if NT = 0, then there is one thread). See
“Legacy Method” on page 645."

> +			__rsvd0		:  4,
> +			apicidsize	:  4,
> +			perftscsize	:  2,
> +			__rsvd1		: 14;
> +	} ecx;
> +	unsigned int sft;
> +
> +	if (tscan->c->extended_cpuid_level < 0x80000008)
> +		return false;
> +
> +	cpuid_leaf_reg(0x80000008, CPUID_ECX, &ecx);
> +
> +	/* If the APIC ID size is 0, then get the shift value from ecx.ncores */
> +	sft = ecx.apicidsize;
> +	if (!sft)
> +		sft = get_count_order(ecx.ncores + 1);
> +
> +	topology_set_dom(tscan, TOPO_CORE_DOMAIN, sft, ecx.ncores + 1);

So yeah, this should be TOPO_SMT_DOMAIN.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette