linux-kernel - Re: Odd performance results

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Date:	Tue, 12 Jul 2016 16:55:51 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	hpa@...or.com, tglx@...utronix.de, mingo@...e.hu,
	ak@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: Odd performance results

On Sun, Jul 10, 2016 at 07:43:27AM -0700, Paul E. McKenney wrote:
> On Sun, Jul 10, 2016 at 07:17:19AM +0200, Peter Zijlstra wrote:
> > 
> > 
> > On 10 July 2016 06:26:39 CEST, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> > >Hello!
> > >
> > >So I ran a quick benchmark which showed stair-step results.  I
> > >immediately
> > >thought "Ah, this is due to CPU 0 and 1, 2 and 3, 4 and 5, and 6 and 7
> > >being threads in a core."  Then I thought "Wait, this is an x86!"
> > >Then I dumped out cpu*/topology/thread_siblings_list, getting the
> > >following:
> > >
> > >	cpu0/topology/thread_siblings_list: 0-1
> > >	cpu1/topology/thread_siblings_list: 0-1
> > >	cpu2/topology/thread_siblings_list: 2-3
> > >	cpu3/topology/thread_siblings_list: 2-3
> > >	cpu4/topology/thread_siblings_list: 4-5
> > >	cpu5/topology/thread_siblings_list: 4-5
> > >	cpu6/topology/thread_siblings_list: 6-7
> > >	cpu7/topology/thread_siblings_list: 6-7
> > 
> > 
> > I'm guessing this is an AMD bulldozer like machine?
> 
> /proc/cpuinfo thinks otherwise:
> 
> processor	: 0
> vendor_id	: GenuineIntel
> cpu family	: 6
> model		: 60
> model name	: Intel(R) Core(TM) i7-4710MQ CPU @ 2.50GHz

Weird, I've never seen an Intel box do that before... hpa, any idea? or
is this just one weird BIOS.