From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id EBA0E2F60D8 for ; Thu, 14 Aug 2025 10:07:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755166083; cv=none; b=A6NpTJIn1ye/gDFK7eXg4C99+SioIR9a2GAhWExQ9IBpYWoVgp5YO0r1P8n3seuQjHE1u+uDdxPvI+UNd7VqFCd/BFz0+mANk46wYBtTDymb8SheaPlHEIXLSzpBiVw+6V+j+EXE1aIDw7bypHnuoDA/gkLhWuXmRrSfsCKrdr0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755166083; c=relaxed/simple; bh=Qf08jHx3sNdCHJcQGcZR42E91SwZm82/gUFqBR8ewsM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=SRLdRUALrQudEu3RAcewCiNs6TJgOlLLRE2OCQaSdIOw0pRIX9Cid/5nW6ZQUYHTAYDJccf5QUohOUGReauq+8CgkxAuymvhyqeAKdop4U49QHjSijEuHnnR1BA5NylYphya9Ww4+sEijXvlG9v1PniQSpy5iBT5UuQFcnWwf24= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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