Path: csiph.com!aioe.org!bofh.it!news.nic.it!robomod From: Peter Zijlstra Newsgroups: linux.kernel Subject: Re: Odd performance results Date: Tue, 12 Jul 2016 21:00:01 +0200 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 31 Organization: linux.* mail to news gateway X-Original-Cc: paulmck@linux.vnet.ibm.com, tglx@linutronix.de, mingo@elte.hu, ak@linux.intel.com, linux-kernel@vger.kernel.org X-Original-Date: Tue, 12 Jul 2016 20:51:20 +0200 X-Original-Message-ID: <20160712185120.GX30909@twins.programming.kicks-ass.net> X-Original-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> <27d2c710-479d-77a9-f2c6-875e9c2bc40f@zytor.com> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1441657 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.