linux-kernel - Re: [patch V3 23/40] x86/cpu: Provide cpu_init/parse

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Message-ID: <03ded839-a746-b741-02dd-c10fe37460bf@amd.com>
Date:   Fri, 4 Aug 2023 13:44:27 +0530
From:   K Prateek Nayak <kprateek.nayak@....com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     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>,
        Michael Kelley <mikelley@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>
Subject: Re: [patch V3 23/40] x86/cpu: Provide cpu_init/parse_topology()

Hello Thomas,

On 8/2/2023 3:51 PM, Thomas Gleixner wrote:
>
> [..snip..]
>
> +static void topo_set_max_cores(struct topo_scan *tscan)
> +{
> +	/*
> +	 * Bug compatible for now. This is broken on hybrid systems:
> +	 * 8 cores SMT + 8 cores w/o SMT
> +	 * tscan.dom_ncpus[TOPO_CORE_DOMAIN] = 24; 24 / 2 = 12 !!
> +	 *
> +	 * Cannot be fixed without further topology enumeration changes.
> +	 */
> +	tscan->c->x86_max_cores = tscan->dom_ncpus[TOPO_CORE_DOMAIN] >>
> +		x86_topo_system.dom_shifts[TOPO_SMT_DOMAIN];
> +}
>

In Documentation/arch/x86/topology.rst, "cpuinfo_x86.x86_max_cores" is
described as "The number of cores in a package". In which case,
shouldn't the above be:

	tscan->c->x86_max_cores = tscan->dom_ncpus[TOPO_PKG_DOMAIN] >>
		x86_topo_system.dom_shifts[TOPO_SMT_DOMAIN];

since, with extended topology, there could be other higher domains and
dom_ncpus[TOPO_CORE_DOMAIN] >> dom_shifts[TOPO_SMT_DOMAIN] should only
give number of cores within the next domain (TOPO_MODULE_DOMAIN).

Am I missing something here?

--
Thanks and Regards,
Prateek