From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E9C04C46470 for ; Wed, 8 Aug 2018 07:59:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 989F1216F3 for ; Wed, 8 Aug 2018 07:59:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="kr7tRlV3" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 989F1216F3 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727109AbeHHKRf (ORCPT ); Wed, 8 Aug 2018 06:17:35 -0400 Received: from merlin.infradead.org ([205.233.59.134]:59642 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726979AbeHHKRf (ORCPT ); Wed, 8 Aug 2018 06:17:35 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=CcJj81gbrsZv5YOLKlSyHb89sgOJWDqb4J9+bqrHXq8=; b=kr7tRlV3W/qfp/feDHkYfO8st BcUQKtp+KCW8ua1APhhFYmp6xjtIUVq/MMi8GJRQVXfknIKHbuXuM/jtJgKH+I8Sw5kpo2T7I1K6w KoagAluX8kWEt4pzng6UzTbtVEWHlAgsw9v9gVewg0SsQCTHz+Zd+PCz52cqS9vTLWX1Nth62cDBN 3pT/vSfg5Zm5LhUP/SLVq2dHKluTsIuCrgqwfFwWAf3u3x/JSAFEX5oDJXw4tGDazOg65+cHJUQ0n zneHvst+ZnBnAefIqd9wkafjG9cc0JI0zDTzjsp0f1oCvM2DHYBtJCX6S2EubO+n3YGxQ1MIRMjpa 2Z8otFCwg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fnJMg-0006NB-A6; Wed, 08 Aug 2018 07:58:42 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 0B4A420437360; Wed, 8 Aug 2018 09:58:41 +0200 (CEST) Date: Wed, 8 Aug 2018 09:58:41 +0200 From: Peter Zijlstra To: Srikar Dronamraju Cc: Ingo Molnar , LKML , Mel Gorman , Rik van Riel , Thomas Gleixner , Michael Ellerman , Heiko Carstens , Suravee Suthikulpanit , Andre Wild Subject: Re: [PATCH] sched/topology: Use Identity node only if required Message-ID: <20180808075840.GO2494@hirez.programming.kicks-ass.net> References: <1533712172-11428-1-git-send-email-srikar@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1533712172-11428-1-git-send-email-srikar@linux.vnet.ibm.com> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 08, 2018 at 12:39:31PM +0530, Srikar Dronamraju wrote: > With Commit 051f3ca02e46 ("sched/topology: Introduce NUMA identity node > sched domain") scheduler introduces an extra numa level. However that > leads to > > - numa topology on 2 node systems no more marked as NUMA_DIRECT. After > this commit, it gets reported as NUMA_BACKPLANE. This is because > sched_domains_numa_level now equals 2 on 2 node systems. > > - Extra numa sched domain that gets added and degenerated on most > machines. The Identity node is only needed on very few systems. > Also all non-numa systems will end up populating > sched_domains_numa_distance and sched_domains_numa_masks tables. > > - On shared lpars like powerpc, this extra sched domain creation can > lead to repeated rcu stalls, sometimes even causing unresponsive > systems on boot. On such stalls, it was noticed that > init_sched_groups_capacity() (sg != sd->groups is always true). The idea was that if the topology level is redundant (as it often is); then the degenerate code would take it out. Why is that not working (right) and can we fix that instead?