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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 751C0C77B7A for ; Thu, 1 Jun 2023 11:56:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232689AbjFAL4z (ORCPT ); Thu, 1 Jun 2023 07:56:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47336 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231651AbjFAL4x (ORCPT ); Thu, 1 Jun 2023 07:56:53 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3B0A7AA; Thu, 1 Jun 2023 04:56:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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=KUMSQwbjndN9y0bHXAp/macV1LggNtVpmB6otmxbyMg=; b=FGJ5kEFZ9Qidvkf/r42AyNan4h FzYOZPi7Pt7wD+f5MJO8wUvFK3eK0hCeUmYW9KmjOEsAsoCCgecIBWSMxsuocsqKb+uRZm+1Z/H7b 8UTuyPUSF+pPmQ8QO+Bn90+FLnsn5T8Tg+68LgK2rdBVU1BF6G3Oz9RdPDNzeapXNx/H0ZJgRgqA6 mxD0Icj8rFWN2OxVS2WqdUswBF6ObWs6Spy+8DUCMk4JaG1GPcvcj8HqXquHGLf10L9O5iHiE7S4c DPxeU5O66rQxL54KwAfsw4arCNjt/kxGszjTPzNGj/tzIi4Zr6/jLgUbGYAuRA148QfCi1i8ExyTL kjBkpuRg==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1q4gv6-00H9MK-1l; Thu, 01 Jun 2023 11:56:44 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id AF501300220; Thu, 1 Jun 2023 13:56:43 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 90255202BDCAC; Thu, 1 Jun 2023 13:56:43 +0200 (CEST) Date: Thu, 1 Jun 2023 13:56:43 +0200 From: Peter Zijlstra To: K Prateek Nayak Cc: linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org, Tejun Heo , x86@kernel.org, Gautham Shenoy Subject: Re: [tip: sched/core] sched/fair: Multi-LLC select_idle_sibling() Message-ID: <20230601115643.GX4253@hirez.programming.kicks-ass.net> References: <168553468754.404.2298362895524875073.tip-bot2@tip-bot2> <3de5c24f-6437-f21b-ed61-76b86a199e8c@amd.com> <20230601111326.GV4253@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230601111326.GV4253@hirez.programming.kicks-ass.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 01, 2023 at 01:13:26PM +0200, Peter Zijlstra wrote: > > This DeathStarBench thing seems to suggest that scanning up to 4 CCDs > isn't too much of a bother; so perhaps something like so? > > (on top of tip/sched/core from just a few hours ago, as I had to 'fix' > this patch and force pushed the thing) > > And yeah, random hacks and heuristics here :/ Does there happen to be > additional topology that could aid us here? Does the CCD fabric itself > have a distance metric we can use? https://www.anandtech.com/show/16529/amd-epyc-milan-review/4 Specifically: https://images.anandtech.com/doci/16529/Bounce-7763.png That seems to suggest there are some very minor distance effects in the CCD fabric. I didn't read the article too closely, but you'll note that the first 4 CCDs have inter-CCD latency < 100 while the rest has > 100. Could you also test on a Zen2 Epyc, does that require nr=8 instead of 4? Should we perhaps write it like: 32 / llc_size ? The Zen2 picture: https://images.anandtech.com/doci/16315/Bounce-7742.png Shows a more pronounced CCD fabric topology, you can really see the 2 CCX inside the CCD but also there's two ligher green squares around the CCDs themselves.