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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 1CF6AC433E0 for ; Wed, 10 Feb 2021 08:12:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D5D1064E42 for ; Wed, 10 Feb 2021 08:12:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233740AbhBJIMT (ORCPT ); Wed, 10 Feb 2021 03:12:19 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44986 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233692AbhBJILh (ORCPT ); Wed, 10 Feb 2021 03:11:37 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4CCD2C061574 for ; Wed, 10 Feb 2021 00:10:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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; bh=y3+x3sZzfjZbRLo0keAbiblQakTQ1YAkfrUq7k/BDqM=; b=WtCgZvqezwm2Y+j5p5s1zs+PUI HoVEgrcIOzGyRPN1iF2GPUu4PFi9HgO6fJSKB2JQvxlzzrwd3p4G4HY7OYgu7C1IjQD8lTXPfIwJx q8VwJ4J5Hq8WbQLOE/veno4JyhYhZfg6bVDcGzRG7hjdq5bryK1og2j4oiyVdJiNWm7Y4nWWXYx6v 6p3V6b82qtyL8wrVmfRrhsEFablIedqsBoTkLsqPtqI94/r4KbxiIikTPdX4CS8nQpBfvdDmqq1LC 8Qaue4uynqWtkIhbGZ1W5reOpKQwF86BRM52y1IjhTms34PHksOLfSDzDfOWPo+rZ1vGMv+lwie/B JwSaTJYA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1l9ka4-008YhV-HN; Wed, 10 Feb 2021 08:10:43 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id A96FA300446; Wed, 10 Feb 2021 09:10:35 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 96C13201D19B1; Wed, 10 Feb 2021 09:10:35 +0100 (CET) Date: Wed, 10 Feb 2021 09:10:35 +0100 From: Peter Zijlstra To: "Luck, Tony" Cc: "Schofield, Alison" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , Dave Hansen , Tim Chen , "H. Peter Anvin" , David Rientjes , Igor Mammedov , Prarit Bhargava , "brice.goglin@gmail.com" Subject: Re: [PATCH] x86, sched: Allow NUMA nodes to share an LLC on Intel platforms Message-ID: References: <20210209223943.9834-1-alison.schofield@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 09, 2021 at 11:09:27PM +0000, Luck, Tony wrote: > > +#define X86_BUG_NUMA_SHARES_LLC X86_BUG(25) /* CPU may enumerate an LLC shared by multiple NUMA nodes */ > > During internal review I wondered why this is a "BUG" rather than a "FEATURE" bit. > > Apparently, the suggestion for "BUG" came from earlier community discussions. > > Historically it may have seemed reasonable to say that a cache cannot span > NUMA domains. But with more and more things moving off the motherboard > and into the socket, this doesn't seem too weird now. If you look at the details this SNC LLC span doesn't behave quite right either. It really isn't a regular cache, but behaves a bit like a mash-up of the s390 book caches and a normal LLC. Did anybody play with adding the book domain to these SNC configurations? Can we detect SNC other than by this quirk?