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

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Message-ID: <87r0o6f8lm.ffs@tglx>
Date:   Mon, 14 Aug 2023 08:20:37 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Zhang, Rui" <rui.zhang@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "Gross, Jurgen" <jgross@...e.com>,
        "mikelley@...rosoft.com" <mikelley@...rosoft.com>,
        "arjan@...ux.intel.com" <arjan@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "ray.huang@....com" <ray.huang@....com>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "Sivanich, Dimitri" <dimitri.sivanich@....com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>
Subject: Re: [patch V3 23/40] x86/cpu: Provide cpu_init/parse_topology()

On Sun, Aug 13 2023 at 16:36, Thomas Gleixner wrote:
> On Sun, Aug 13 2023 at 13:30, Rui Zhang wrote:
>>> My understanding is that, to ensure a package scope unique core_id,
>>> rather than Module/Tile scope unique, what is really needed here is
>>> something like,
>>>>
>>>         apicid >>= x86_topo_system.dom_shifts[SMT];
>>>         c->topo.core_id = apicid & (x86_topo_system.dom_size[PACKAGE]
>>> - 1);

Actually it needs to be:

         apicid &= (1U << x86_topo_system.dom_shifts[TOPO_PKG_DOMAIN]) - 1;
         c->topo.core_id = apicid >> x86_topo_system.dom_shifts[TOPO_SMT_DOMAIN];

because otherwise you shift the lowest package ID bit into the result.