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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C6DA4CA0EE8 for ; Thu, 14 Aug 2025 13:15:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=R1p5sG6Up5RyX/VDuTRVHBTUjLDvCuikysszartwlsw=; b=CVGCigDjn0+UmL/JTNsP231KLo 7eR38eap7b3fomBvSc5xtor3ULKNrdH4/wzei7NiqkOguC5nrnSyxCkEYyuSXoKPJCAmIAD/S2SCJ k5NMGZnJVWv7kelM7iuuoWS8cnARSnlvWQ1jxH4VmPS0RGV5JzzMszdnH3//fUDZPj0FfrJIWdSKq ezGhs1FyZCv1PAaShZZjE6qKTtbBRrLnr30yoVPXVPFVGXcpHSP5izkYrIEqDyOlJ1lfK6ohvZu5q p5LVwh0ScUBO1q7km4S+SZyMgCrG8iocjnl+A9lrrbgrHgfA9d0eA3XNcdP4jf6JjHbb1fh/S6BNE cUbTI48A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1umXnT-0000000GyMC-3ITJ; Thu, 14 Aug 2025 13:15:11 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1umUsJ-0000000GWbc-2OJT for linux-arm-kernel@lists.infradead.org; Thu, 14 Aug 2025 10:08:00 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BECDB1691; Thu, 14 Aug 2025 03:07:50 -0700 (PDT) Received: from bogus (e133711.arm.com [10.1.196.55]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0A0E53F738; Thu, 14 Aug 2025 03:07:55 -0700 (PDT) Date: Thu, 14 Aug 2025 11:07:53 +0100 From: Sudeep Holla To: "Christoph Lameter (Ampere)" Cc: Jeremy Linton , Huang Shijie , Sudeep Holla , catalin.marinas@arm.com, will@kernel.org, patches@amperecomputing.com, Shubhang@os.amperecomputing.com, krzysztof.kozlowski@linaro.org, bjorn.andersson@oss.qualcomm.com, geert+renesas@glider.be, arnd@arndb.de, nm@ti.com, ebiggers@kernel.org, nfraprado@collabora.com, prabhakar.mahadev-lad.rj@bp.renesas.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm64: defconfig: enable CONFIG_SCHED_CLUSTER Message-ID: References: <20250808025533.6422-1-shijie@os.amperecomputing.com> <2d9259e4-1b58-435d-bf02-9c4badd52fd9@arm.com> <20250813-gifted-nimble-wildcat-6cdf65@sudeepholla> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250814_030759_657931_FEE90C54 X-CRM114-Status: GOOD ( 22.97 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Aug 13, 2025 at 08:55:36AM -0700, Christoph Lameter (Ampere) wrote: > On Wed, 13 Aug 2025, Sudeep Holla wrote: > > > > The problem is that this information is being sourced from the ACPI PPTT. > > > The ACPI specification (AFAIK) doesn't define a cluster, so the linux > > > cluster information is being 'invented' based on however the firmware vendor > > > choose to group CPU nodes in the PPTT. Which means its possible for them to > > > unknowingly create clusters, or also fail to create them when they make > > > sense. > > > > +1, completely agree. As Jeremy mentioned, it is hit or miss and cluster > > is loosely defined and IIRC Huawei pushed this based on their platform at > > the time and it did break some benchmarks on few other platforms. So it > > is not a good idea to make it default config IMO. > > Can we figure out which platforms benchmarks were affected and why? > I am not sure on either. One way to figure out the affected platforms is to merge this change and expect the platform users/maintainers to report. > It seems the notion of a "cluster" on ARM64 is derived (I guess a better > word than "invented" hehe) from sibling information instead of PPTT. But > using that information should work fine right? > I have my doubts but I may be wrong. As mentioned in the other email in this thread, "cluster" IMO is ill-defined both in ACPI and Arm architecture which is the root cause for all the issue around it. -- Regards, Sudeep