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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (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 3AAE3C021B8 for ; Tue, 4 Mar 2025 08:25:50 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4Z6TK85m3pz2ykZ; Tue, 4 Mar 2025 19:25:48 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; arc=none smtp.remote-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1741076748; cv=none; b=Js3QzCWXib9G4PVvKkKuDJ4HjpPiPB/8ZcN9H+PpgYFMkff1c247C88krUeIDmeOA24qP1umwwuqJkFR9SQW3Gb5zxLAe4CCo+OFm+iscoLKyGWHld5T6VOX2v4zh50iqukGi7crpqNSBpXjNd3W2skeiY0xDBbGJca2BocGxR6lP+oe+n9BAj/I/wwP7EgrljJH67Uw/pPl/63o/T8i5Kz6VCcSaYwYSWZ5Ai/OUuyXnsDkYlcTekpeBFdtqHb9kcVWcrk+7uJ2Qp2gQkmknnLyJkm6h3ktXu/WD3BKdKMgbFxlH/1jYRMP5ypLNfYTqVBrbROiLFXy1qMKzTJ35Q== ARC-Message-Signature: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1741076748; c=relaxed/relaxed; bh=BPyo6yazjyUnhJj+joZfTPzFqELUcAwTIbrDY0AFd8k=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=k6AdjvhYttekPDZV3GWNU9osyjyrEZD2oezDzDKmQotUGFMK0uQ5Hovp4nIymsYF58lng094M4AOPs/dAS+a5fqISHJ75sl1jtc+v7Ce8nUfVaReVFViQTCYkbA5nVpUyYPoGtHo1HObzjMQrxai13I4aCm5s5QulVDPB+2V1WLYJGveU2ytHw7pYtX0lKnJnJeoB/YGsjl21YrGLqe6q1KfWhgmoVUE55D8KEfjKd+uSl+bTuERxibf6c3Jt0RLGANtV8m8DDPmfKn2yzuY0/HAzEjn2+E2AsMKXXTlJ5+pPSBxDQtB3WZxNmk1G+9hxASIE2CF2vBH+h6ffrsLJg== ARC-Authentication-Results: i=1; lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass (client-ip=217.140.110.172; helo=foss.arm.com; envelope-from=pierre.gondois@arm.com; receiver=lists.ozlabs.org) smtp.mailfrom=arm.com Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=arm.com (client-ip=217.140.110.172; helo=foss.arm.com; envelope-from=pierre.gondois@arm.com; receiver=lists.ozlabs.org) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lists.ozlabs.org (Postfix) with ESMTP id 4Z6TK75jY9z2yHj for ; Tue, 4 Mar 2025 19:25:45 +1100 (AEDT) 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 634871063; Tue, 4 Mar 2025 00:25:27 -0800 (PST) Received: from [10.34.129.29] (unknown [10.34.129.29]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A5ACD3F66E; Tue, 4 Mar 2025 00:25:08 -0800 (PST) Message-ID: <2fdea4f6-db98-4dc7-947f-e19ee54d2c3c@arm.com> Date: Tue, 4 Mar 2025 09:25:02 +0100 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 3/4] arm64: topology: Support SMT control on ACPI based system To: Yicong Yang , Sudeep Holla Cc: yangyicong@hisilicon.com, catalin.marinas@arm.com, will@kernel.org, tglx@linutronix.de, peterz@infradead.org, mpe@ellerman.id.au, linux-arm-kernel@lists.infradead.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, dietmar.eggemann@arm.com, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, morten.rasmussen@arm.com, msuchanek@suse.de, gregkh@linuxfoundation.org, rafael@kernel.org, jonathan.cameron@huawei.com, prime.zeng@hisilicon.com, linuxarm@huawei.com, xuwei5@huawei.com, guohanjun@huawei.com, sshegde@linux.ibm.com References: <20250218141018.18082-1-yangyicong@huawei.com> <20250218141018.18082-4-yangyicong@huawei.com> <336e9c4e-cd9c-4449-ba7b-60ee8774115d@arm.com> <20250228190641.q23vd53aaw42tcdi@bogus> <32e572d6-dedd-d8a3-13be-6de02303a64d@huawei.com> Content-Language: en-US From: Pierre Gondois In-Reply-To: <32e572d6-dedd-d8a3-13be-6de02303a64d@huawei.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 3/3/25 15:40, Yicong Yang wrote: > On 2025/3/3 19:16, Sudeep Holla wrote: >> On Mon, Mar 03, 2025 at 10:56:12AM +0100, Pierre Gondois wrote: >>> On 2/28/25 20:06, Sudeep Holla wrote: >>>>>> >>>>>> Ditto as previous patch, can get rid if it is default 1. >>>>>> >>>>> >>>>> On non-SMT platforms, not calling cpu_smt_set_num_threads() leaves >>>>> cpu_smt_num_threads uninitialized to UINT_MAX: >>>>> >>>>> smt/active:0 >>>>> smt/control:-1 >>>>> >>>>> If cpu_smt_set_num_threads() is called: >>>>> active:0 >>>>> control:notsupported >>>>> >>>>> So it might be slightly better to still initialize max_smt_thread_num. >>>>> >>>> >>>> Sure, what I meant is to have max_smt_thread_num set to 1 by default is >>>> that is what needed anyways and the above code does that now. >>>> >>>> Why not start with initialised to 1 instead ? >>>> Of course some current logic needs to change around testing it for zero. >>>> >>> >>> I think there would still be a way to check against the default value. >>> If we have: >>> unsigned int max_smt_thread_num = 1; >>> >>> then on a platform with 2 threads, the detection condition would trigger: >>> xa_for_each(&hetero_cpu, hetero_id, entry) { >>> if (entry->thread_num != max_smt_thread_num && max_smt_thread_num) <---- (entry->thread_num=2) and (max_smt_thread_num=1) >>> pr_warn_once("Heterogeneous SMT topology is partly >>> supported by SMT control\n"); >>> >>> so we would need an additional variable: >>> bool is_initialized = false; >> >> Sure, we could do that or skip the check if max_smt_thread_num == 1 ? >> >> I mean >> if (entry->thread_num != max_smt_thread_num && max_smt_thread_num != 1) >> I think it will be problematic if we parse: - first a CPU with 1 thread - then a CPU with 2 threads in that case we should detect the 'Heterogeneous SMT topology', but we cannot because we don't know whether max_smt_thread_num=1 because 1 is the default value or we found a CPU with one thread.