linux-kernel - Odd performance results

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Message-Id: <20160710042639.GA4068@linux.vnet.ibm.com>
Date:	Sat, 9 Jul 2016 21:26:39 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	peterz@...radead.org, hpa@...or.com, tglx@...utronix.de,
	mingo@...e.hu, ak@...ux.intel.com
Cc:	linux-kernel@...r.kernel.org
Subject: Odd performance results

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

Is this now expected behavior or a fluke of my particular laptop?  Here is
hoping for expected behavior, as it makes NUMA locality the default for
a great many workloads.

Enlightenment?

							Thanx, Paul