Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752973AbcJJQqW (ORCPT ); Mon, 10 Oct 2016 12:46:22 -0400 Received: from mga01.intel.com ([192.55.52.88]:5835 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752475AbcJJQqV (ORCPT ); Mon, 10 Oct 2016 12:46:21 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.31,325,1473145200"; d="scan'208";a="888566949" Date: Mon, 10 Oct 2016 09:45:44 -0700 From: "Luck, Tony" To: Nilay Vaish Cc: Fenghua Yu , Thomas Gleixner , "H. Peter Anvin" , Ingo Molnar , Peter Zijlstra , Stephane Eranian , Borislav Petkov , Dave Hansen , Shaohua Li , David Carrillo-Cisneros , Ravi V Shankar , Sai Prakhya , Vikas Shivappa , linux-kernel , x86 Subject: Re: [PATCH v3 01/18] Documentation, ABI: Add a document entry for cache id Message-ID: <20161010164543.GA30442@intel.com> References: <1475894763-64683-1-git-send-email-fenghua.yu@intel.com> <1475894763-64683-2-git-send-email-fenghua.yu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1064 Lines: 28 On Sat, Oct 08, 2016 at 12:11:08PM -0500, Nilay Vaish wrote: > On 7 October 2016 at 21:45, Fenghua Yu wrote: > > From: Fenghua Yu > > + caches typically exist per core, but there may not be a > > + power of two cores on a socket, so these caches may be > > + numbered 0, 1, 2, 3, 4, 5, 8, 9, 10, ... > > + > > While it is ok that the caches are not numbered contiguously, it is > unclear how this is related to number of cores on a socket being a > power of 2 or not. That's a side effect of the x86 algorithm to generate the unique ID which uses a shift to put the socket number in some upper bits while leaving the "id within a socket" in the low bits. I don't think it worth documenting here, but I noticed that we don't keep the IDs within a core contguous either. On my 24 core Broadwell they are not 0 ... 23 then a gap from 24 to 31. I actually have on socket 0: 0, 1, 2, 3, 4, 5 8, 9, 10, 11, 12, 13 16, 17, 18, 19, 20, 21 24, 25, 26, 27, 28, 29 -Tony