linux-kernel - Re: [CRM114spam]: Re: Odd performance results

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Message-ID: <20160712191049.GB27918@gallifrey>
Date:	Tue, 12 Jul 2016 20:10:49 +0100
From:	"Dr. David Alan Gilbert" <dave@...blig.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>, paulmck@...ux.vnet.ibm.com,
	tglx@...utronix.de, mingo@...e.hu, ak@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: Re: [CRM114spam]: Re: Odd performance results

* Peter Zijlstra (peterz@...radead.org) wrote:
> On Tue, Jul 12, 2016 at 10:49:58AM -0700, H. Peter Anvin wrote:
> > On 07/12/16 08:05, Paul E. McKenney wrote:
> > The CPU in question (and /proc/cpuinfo should show this) has four cores
> > with a total of eight threads.  The "siblings" and "cpu cores" fields in
> > /proc/cpuinfo should show the same thing.  So I am utterly confused
> > about what is unexpected here?
> 
> Typically threads are enumerated differently on Intel parts. Namely:
> 
> 	cpu_id = code_id + nr_cores * smt_id
> 
> which gives, for a 4 core, 2 thread part:
> 
> 	0-3: core 0-3, smt0
> 	4-7: core 0-3, smt1
> 
> My Core i7-2600k for example has:
> 
> $ cat /sys/devices/system/cpu/cpu*/topology/thread_siblings_list
> 0,4
> 1,5
> 2,6
> 3,7
> 0,4
> 1,5
> 2,6
> 3,7
> 
> The ordering Paul has, namely 0,1 for core0,smt{0,1} is not something
> I've ever seen on an Intel part. AMD otoh does enumerate their CMT stuff
> like what Paul has.

Paul's isn't unique:
cat /sys/devices/system/cpu/cpu*/topology/thread_siblings_list
0-1
0-1
2-3
2-3

i7-3520M CPU @ 2.90GHz   (Dual core with hyperthread, Thinkpad t530, fedora 24)

Dave
-- 
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