linux-kernel - Re: [PATCH] x86/smpboot: Fix __max_logical

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Message-ID: <ffcc96a9-253d-4e78-d2a2-0a30972a2d60@redhat.com>
Date:   Thu, 7 Sep 2017 17:18:23 -0400
From:   Prarit Bhargava <prarit@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Jean Delvare <jdelvare@...e.com>, Borislav Petkov <bp@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>
Subject: Re: [PATCH] x86/smpboot: Fix __max_logical_packages estimate



On 09/06/2017 02:36 PM, Prarit Bhargava wrote:
> A system booted with a small number of cores enabled per package
> panics because the estimate of __max_logical_packages is too low.
> This occurs when the total number of active cores across all packages
> is less than the maximum core count for a single package.
> 
> ie) On a 4 package system with 20 cores/package where only 4 cores
> are enabled on each package, the value of __max_logical_packages is
> calculated as DIV_ROUND_UP(16 / 20) = 1 and not 4.
> 
> Improve the estimate of __max_logical_packages by comparing the current
> estimate to the number of SMBIOS type 4 Processor Information structures.
> If __max_logical_packages is still insufficient during boot use the largest
> possible value of Package ID.

If I move this calculation to native_smp_cpus_done() I can eliminate a chunk
of code and use boot_cpu_data.booted_cores to get a correct value.

I'll resubmit with a new patch.

P.