From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751867AbdKLQzb (ORCPT ); Sun, 12 Nov 2017 11:55:31 -0500 Received: from mx1.redhat.com ([209.132.183.28]:53320 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751651AbdKLQz3 (ORCPT ); Sun, 12 Nov 2017 11:55:29 -0500 Subject: Re: [PATCH v5 2/3] x86/topology: Avoid wasting 128k for package id array To: Thomas Gleixner , Andi Kleen References: <20171105165428.32108-1-prarit@redhat.com> <20171105165428.32108-3-prarit@redhat.com> <372083ad-2a77-4646-bc67-dd4348a521d9@redhat.com> <20171110150112.GI8522@tassilo.jf.intel.com> Cc: linux-kernel@vger.kernel.org, Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Peter Zijlstra , Dave Hansen , Piotr Luc , Kan Liang , Borislav Petkov , Stephane Eranian , Arvind Yadav , Andy Lutomirski , Christian Borntraeger , "Kirill A. Shutemov" , Tom Lendacky , He Chen , Mathias Krause , Tim Chen , Vitaly Kuznetsov From: Prarit Bhargava Message-ID: Date: Sun, 12 Nov 2017 11:55:25 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Sun, 12 Nov 2017 16:55:28 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/12/2017 08:36 AM, Thomas Gleixner wrote: > On Fri, 10 Nov 2017, Andi Kleen wrote: >>>> All of that works. There is no way to make sure that a lookup is fully >>>> serialized against a concurrent update. Even if the lookup holds >>>> cpu_read_lock() the new package might arrive right after the unlock. >>>> >>> >>> Thanks Thomas. >>> >>> Andi, do you want to take a look at this? >> >> I was originally worried about races, that is why i tried to put >> everything into cpu_data. But that didn't work out because something >> clears it. Perhaps the right solution would be some extra per_cpu >> data variables, and search for the first match. I suspect that would >> be simpler. But if that doesn't work I guess something like Thomas' >> example will work. > > Sure, we can use a separate per cpu variable. The race for looking up phys > -> logical will always be there if that handles stuff like the uncore PCI > physid one. There is not much which can prevent that. > > The other option is to figure out what clears cpu_data on online and just > preserve the logical/physcial translation across that clear. > > One thing you need to be careful about (in both cases) is the value. The > data is zeroed on boot, so we either need to fill that with UINT_MAX at > boot time in one of the functions which does a for_each_possible_cpu() loop > anyway or just leave 0 as the 'not initialized' value and make the first > logical package be '1'. The readout functions (percpu, translation, > etc.) just can subtract 1. I'll look into this (code & test) and get back with a v6. Thanks Thomas, P. > > Thanks, > > tglx >