linux-kernel - Re: [PATCH] x86/amd: Fixup cpu_core_id for family17h downcore configuration

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Message-ID: <20170720083523.GA18515@nazgul.tnic>
Date:   Thu, 20 Jul 2017 10:35:23 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, peterz@...radead.org,
        Yazen.Ghannam@....com
Subject: Re: [PATCH] x86/amd: Fixup cpu_core_id for family17h downcore
 configuration

On Thu, Jul 20, 2017 at 03:29:28AM -0500, Suravee Suthikulpanit wrote:
> For family17h, current cpu_core_id is directly taken from the value
> CPUID_Fn8000001E_EBX[7:0] (CoreId), which is the physical ID of the
> core within a die. However, on system with downcore configuration
> (where not all physical cores within a die are available),
> this could result in the case where cpu_core_id > (cores_per_node - 1).
> 
> Fix up the cpu_core_id by breaking down the bitfields of CoreId,
> and calculate relative ID using available topology information.
> 
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> ---
>  arch/x86/kernel/cpu/amd.c | 61 ++++++++++++++++++++++++++++++++++-------------
>  1 file changed, 45 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index bb5abe8..e7de105 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -310,38 +310,67 @@ static void amd_get_topology(struct cpuinfo_x86 *c)
>  
>  	/* get information required for multi-node processors */
>  	if (boot_cpu_has(X86_FEATURE_TOPOEXT)) {

Please carve this whole TOPOEXT-specific logic out, into a separate
function, say __get_topoext() or so, for better readability/easier
review.

Thanks.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--