linux-kernel - Re: [patch v5 03/19] x86/cpu: Add legacy topology parser

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Date: Wed, 24 Jan 2024 21:12:58 +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 03/19] x86/cpu: Add legacy topology parser

On Tue, Jan 23, 2024 at 01:53:34PM +0100, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> The legacy topology detection via CPUID leaf 4, which provides the number
> of cores in the package and CPUID leaf 1 which provides the number of
> logical CPUs in case that FEATURE_HT is enabled and the CMP_LEGACY feature
> is not set, is shared for Intel, Centaur amd Zhaoxin CPUs.
					   ^^^

x86 maintainer Freudian slip. :-P

Happens to me too.

> Lift the code from common.c without the early detection hack and provide it
> as common fallback mechanism.
> 
> Will be utilized in later changes.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Tested-by: Juergen Gross <jgross@...e.com>
> Tested-by: Sohil Mehta <sohil.mehta@...el.com>
> Tested-by: Michael Kelley <mhklinux@...look.com>
> 
> 
> ---
>  arch/x86/kernel/cpu/common.c          |    3 ++
>  arch/x86/kernel/cpu/topology.h        |    3 ++
>  arch/x86/kernel/cpu/topology_common.c |   46 +++++++++++++++++++++++++++++++++-
>  3 files changed, 51 insertions(+), 1 deletion(-)
> ---
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -891,6 +891,9 @@ void detect_ht(struct cpuinfo_x86 *c)
>  #ifdef CONFIG_SMP
>  	int index_msb, core_bits;
>  
> +	if (topo_is_converted(c))
> +		return;
> +
>  	if (detect_ht_early(c) < 0)
>  		return;
>  
> --- a/arch/x86/kernel/cpu/topology.h
> +++ b/arch/x86/kernel/cpu/topology.h
> @@ -6,6 +6,9 @@ struct topo_scan {
>  	struct cpuinfo_x86	*c;
>  	unsigned int		dom_shifts[TOPO_MAX_DOMAIN];
>  	unsigned int		dom_ncpus[TOPO_MAX_DOMAIN];
> +
> +	// Legacy CPUID[1]:EBX[23:16] number of logical processors

Can we pretty please use the good 'ol multi-line comment style and not
turn tip into a mess with a mixture between single-line and multi-line
comments?

Thanks.

> +	unsigned int		ebx1_nproc_shift;
>  };
>  
>  bool topo_is_converted(struct cpuinfo_x86 *c);


-- 
Regards/Gruss,
    Boris.

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