From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753732AbdLVMbI (ORCPT ); Fri, 22 Dec 2017 07:31:08 -0500 Received: from mx2.suse.de ([195.135.220.15]:49280 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751770AbdLVMbG (ORCPT ); Fri, 22 Dec 2017 07:31:06 -0500 Date: Fri, 22 Dec 2017 13:31:03 +0100 From: Michal Hocko To: kemi Cc: Greg Kroah-Hartman , Andrew Morton , Vlastimil Babka , Mel Gorman , Johannes Weiner , Christopher Lameter , YASUAKI ISHIMATSU , Andrey Ryabinin , Nikolay Borisov , Pavel Tatashin , David Rientjes , Sebastian Andrzej Siewior , Dave , Andi Kleen , Tim Chen , Jesper Dangaard Brouer , Ying Huang , Aaron Lu , Aubrey Li , Linux MM , Linux Kernel Subject: Re: [PATCH v2 3/5] mm: enlarge NUMA counters threshold size Message-ID: <20171222123103.GP4831@dhcp22.suse.cz> References: <1513665566-4465-1-git-send-email-kemi.wang@intel.com> <1513665566-4465-4-git-send-email-kemi.wang@intel.com> <20171219124045.GO2787@dhcp22.suse.cz> <439918f7-e8a3-c007-496c-99535cbc4582@intel.com> <20171220101229.GJ4831@dhcp22.suse.cz> <268b1b6e-ff7a-8f1a-f97c-f94e14591975@intel.com> <20171221081706.GA4831@dhcp22.suse.cz> <1fb66dfd-b64c-f705-ea27-a9f2e11729a4@intel.com> <20171221085952.GB4831@dhcp22.suse.cz> <10bf5ed1-77f0-281b-dde5-282879e87c39@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <10bf5ed1-77f0-281b-dde5-282879e87c39@intel.com> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 21-12-17 18:31:19, kemi wrote: > > > On 2017年12月21日 16:59, Michal Hocko wrote: > > On Thu 21-12-17 16:23:23, kemi wrote: > >> > >> > >> On 2017年12月21日 16:17, Michal Hocko wrote: > > [...] > >>> Can you see any difference with a more generic workload? > >>> > >> > >> I didn't see obvious improvement for will-it-scale.page_fault1 > >> Two reasons for that: > >> 1) too long code path > >> 2) server zone lock and lru lock contention (access to buddy system frequently) > > > > OK. So does the patch helps for anything other than a microbenchmark? > > > >>>> Some thinking about that: > >>>> a) the overhead due to cache bouncing caused by NUMA counter update in fast path > >>>> severely increase with more and more CPUs cores > >>> > >>> What is an effect on a smaller system with fewer CPUs? > >>> > >> > >> Several CPU cycles can be saved using single thread for that. > >> > >>>> b) AFAIK, the typical usage scenario (similar at least)for which this optimization can > >>>> benefit is 10/40G NIC used in high-speed data center network of cloud service providers. > >>> > >>> I would expect those would disable the numa accounting altogether. > >>> > >> > >> Yes, but it is still worthy to do some optimization, isn't? > > > > Ohh, I am not opposing optimizations but you should make sure that they > > are worth the additional code and special casing. As I've said I am not > > convinced special casing numa counters is good. You can play with the > > threshold scaling for larger CPU count but let's make sure that the > > benefit is really measurable for normal workloads. Special ones will > > disable the numa accounting anyway. > > > > I understood. Could you give me some suggestion for those normal workloads, Thanks. > I will have a try and post the data ASAP. Well, to be honest, I am really confused what is your objective for these optimizations then. I hope we have agreed that workloads which really need to squeeze every single CPU cycle in the allocation path will simply disable the whole numa stat thing. I haven't yet heard about any use case which would really required numa stats and suffer from the numa stats overhead. I can see some arguments for a better threshold scaling but that requires to check wider range of tests to show there are no unintended changes. I am not really confident you understand that when you are asking for "those normal workloads". So please, try to step back, rethink who you are optimizing for and act accordingly. If I were you I would repost the first patch which only integrates numa stats because that removes a lot of pointless code and that is a win of its own. -- Michal Hocko SUSE Labs