linux-kernel - Re: [PATCH 2/3] x86/topology: Fix AMD core count

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Date:	Tue, 22 Mar 2016 03:10:15 -0500
From:	Sherry Hurwitz <sherry.hurwitz@....com>
To:	Borislav Petkov <bp@...en8.de>, Huang Rui <ray.huang@....com>
CC:	Peter Zijlstra <peterz@...radead.org>, <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>, <mingo@...nel.org>,
	<aherrmann@...e.com>, <jencce.kernel@...il.com>,
	Gang Long <gang.long@....com>
Subject: Re: [PATCH 2/3] x86/topology: Fix AMD core count

On 03/21/2016 08:57 AM, Borislav Petkov wrote:
> +- AMD: the number of cores in a processor. On a system where cores are
> +clustered in groups of 2, 4 or more in compute units, this variable
> +denotes the number of*compute units*  on the node.
> +
> +In both cases, the number of scheduling threads is computed by doing:
> +
> +	x86_max_cores * smp_num_siblings
> +
> +This means:
> +
> +* smp_num_siblings: the number of siblings in a core. On AMD with
> +compute units, this number is the number of compute unit siblings,
> +i.e., compute unit cores in a single compute unit, according to their
> +nomenclature.
> -- hr
Boris, this documentation will help tremendously.  In just this line of 
code:

nr_local_cpus = nr_cores * nr_siblings

we have an Intel HT = AMD core = logical_cpu
and core = AMD compute unit.

Anybody surprised there was a bug?

The surprising thing is that running lscpu on a 32 core 2 socket 6300 
Opteron system without
the patches I get the same output as with the patches and it matches 
Ray's.  I don't see an impact.