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

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Message-ID: <20160321094611.GB26555@hr-amur2>
Date:	Mon, 21 Mar 2016 17:46:12 +0800
From:	Huang Rui <ray.huang@....com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Borislav Petkov <bp@...en8.de>,
	Sherry Hurwitz <sherry.hurwitz@....com>, <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 Mon, Mar 21, 2016 at 09:21:29AM +0100, Peter Zijlstra wrote:
> On Mon, Mar 21, 2016 at 11:07:46AM +0800, Huang Rui wrote:
> > > > The issue is that Linux assumes:
> > > > 
> > > > 	nr_logical_cpus = nr_cores * nr_siblings
> > > > 
> > > > But AMD reports its CU unit as 2 cores, but then sets num_smp_siblings
> > > > to 2 as well.
> 
> > But I am confused with c->x86_max_cores /= smp_num_siblings, what is
> > the real meaning of c->x86_max_cores here for AMD, the whole compute
> > unit numbers per socket?
> 
> Yes, with the whole Compute Unit being the Core, each logical CPU
> becomes a Thread. This is the direct consequence of using the SMT
> topology to model the CU thing.
> 

OK, maybe, we would better add a comment to explain here. :-)

Thanks,
Rui