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 A77BEC77B7E for ; Thu, 1 Jun 2023 14:51:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233953AbjFAOvY (ORCPT ); Thu, 1 Jun 2023 10:51:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36214 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233476AbjFAOvW (ORCPT ); Thu, 1 Jun 2023 10:51:22 -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 33C12C0; Thu, 1 Jun 2023 07:51:19 -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=1JQ8H5SWLeF9hOjl0b6jkGrksawhL5bRI40mRJFX8jI=; b=AQipA1TAR5OQm4luUa3IrhuR+Q FgALeD2E/Nc+RT2aOlQFunr2BdKZkbGkQ7Q+nDWwOFxAJWAaWXg/8NU6mvJng/EZ1Fc+rMaF9yq3N dNO6Kh1F4gAbUz3hz/m/xU129pQ12UMkZbg8sAcvVmzn+P9/B7xN7QLozGANCPwRAmnweqK4Vonnd d1oNWX0fJDB3PbN7wHOov41U6yqHvMD/hEE78WiE0T2vIXe6rfTKY51/wUJGVaHCggdJWLyL7aavQ iIQmdoxx1BNYf+EoXMQ705PGwT0Hwzjg0c7j5eAX1xi0QymrQD/YJ3CfXFsmi/6MzM9RthImW4J5B g6i9DJtA==; 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 1q4jdz-00HB7j-0r; Thu, 01 Jun 2023 14:51:15 +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 ED838300269; Thu, 1 Jun 2023 16:51:13 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id CFD43202BDCAC; Thu, 1 Jun 2023 16:51:13 +0200 (CEST) Date: Thu, 1 Jun 2023 16:51:13 +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: <20230601145113.GA559993@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> <20230601115643.GX4253@hirez.programming.kicks-ass.net> <20230601120001.GJ38236@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230601120001.GJ38236@hirez.programming.kicks-ass.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 01, 2023 at 02:00:01PM +0200, Peter Zijlstra wrote: > On Thu, Jun 01, 2023 at 01:56:43PM +0200, Peter Zijlstra wrote: > > 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. > > I can't seem to find pretty pictures for Zen4 Epyc; what does that want? > That's even bigger at 96/8=12 LLCs afaict. Going by random pictures on the interweb again, it looks like this Zen4 thing wants either 2 groups of 6 each, or 4 groups of 3. But you have the hardware, so I'll let you figure it out.