Odd performance results

From: Paul E. McKenney
Date: Sun Jul 10 2016 - 00:26:44 EST


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