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 5E9DCC021B8 for ; Tue, 4 Mar 2025 08:34:44 +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:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=BPyo6yazjyUnhJj+joZfTPzFqELUcAwTIbrDY0AFd8k=; b=mDZLJdAX85/CSJIxUC5PCQDLB/ STxf+53ipIXKN/QsMTb/NGtpAPXpYqT6zxR3XSVXTgwwFMtp/JHi7nX1mtEcf96cnGkwAtJYGNoes TriuIN43cAqZWuAUYGhIELRLb+Ir2ync67te1x+RXyK9PQby/Cw4bOeHt1N9z+9VfFSC8Kyq9N7bl i07+giSJvsTu9zAjRbW5TathG/34GvrhSJznDYUqDKl2GKKNlaXN6tluEl87n0NMUN1+u1lr8VUa8 TNY7Lii/jwN7F1yAFgjLOSY3NzN5qKsMUbRgwOcGDTftEKKHviZt0vGmVYx/v07jvSZZFzPye1MZs hvkU8DdA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tpNjZ-00000003fCs-37J7; Tue, 04 Mar 2025 08:34:37 +0000 Received: from casper.infradead.org ([2001:8b0:10b:1236::1]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tpNb4-00000003cwG-06xm for linux-arm-kernel@bombadil.infradead.org; Tue, 04 Mar 2025 08:25:50 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Transfer-Encoding:Content-Type: In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date:Message-ID:Sender :Reply-To:Content-ID:Content-Description; bh=BPyo6yazjyUnhJj+joZfTPzFqELUcAwTIbrDY0AFd8k=; b=bS6H40DA9nMI8ZpclYxzzPO4CM dMpt8uNSTCMvJeJw3WsxuBo/M1ttieYd9bI+v79CIzTPUPa8fTa1vpVO8TV+4n9w5j9qb8SKAo9Rr 4U/0n3OQbgIFhVCkgGW/vp9Jyw/q80rb0zHByeLaJqNxWfwv0ILH50MkxPw76U5eyXc+FgCtuGAbt mjJD4pBBCICl2FYKO6JAkoFKT6vCKj/fAevmrWs7s7zpS2URP5P3//FlfS9vLSOi1jme4/2F7pH/t 6zU6XoVsF+ne3CyV0pLVE41cYFW4QXVO1MyvnFxQ7jl6Y3WkXA2q5RIwMOthg+5aW9RzJgZdUWGhK 1kHHMB7A==; Received: from foss.arm.com ([217.140.110.172]) by casper.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tpNb1-00000000RAh-0Xwu for linux-arm-kernel@lists.infradead.org; Tue, 04 Mar 2025 08:25:48 +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 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 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250304_082547_301016_D87D8FE0 X-CRM114-Status: GOOD ( 14.08 ) 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 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.