From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750863AbcGLRwu (ORCPT ); Tue, 12 Jul 2016 13:52:50 -0400 Received: from terminus.zytor.com ([198.137.202.10]:52722 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750758AbcGLRwt (ORCPT ); Tue, 12 Jul 2016 13:52:49 -0400 Subject: Re: Odd performance results To: paulmck@linux.vnet.ibm.com, Peter Zijlstra References: <20160710042639.GA4068@linux.vnet.ibm.com> <7DF218CD-22F6-4E46-A628-2138AEA3A161@infradead.org> <20160710144327.GX4650@linux.vnet.ibm.com> <20160712145551.GU30909@twins.programming.kicks-ass.net> <20160712150529.GN7094@linux.vnet.ibm.com> Cc: tglx@linutronix.de, mingo@elte.hu, ak@linux.intel.com, linux-kernel@vger.kernel.org From: "H. Peter Anvin" Message-ID: <27d2c710-479d-77a9-f2c6-875e9c2bc40f@zytor.com> Date: Tue, 12 Jul 2016 10:49:58 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <20160712150529.GN7094@linux.vnet.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/12/16 08:05, Paul E. McKenney wrote: > On Tue, Jul 12, 2016 at 04:55:51PM +0200, Peter Zijlstra wrote: >> 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" 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. > > ;-) > > It is a Lenovo W541 laptop, for whatever that might be worth. Roughly > on year old. > Well, the obvious thing here is that CPUs 0-1, 2-3, 4-5, and 6-7 *are* indeed threads in a core... Intel x86 products have supported multithreading since the Pentium 4. So the "wait, this is an x86!" bit is strange to me. 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? Also, you mentioned absolutely nothing about what kind of benchmark it was, or what the "stairstepping" results imply, so it doesn't really make it any easier... -hpa