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 55FE2C2D1 for ; Tue, 4 Mar 2025 10:02:38 +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=1741082560; cv=none; b=BA3u/iwpHrIvYvK8ppivxMD4Sof35JNtg4YuoCl4UlnZdUFv6k26zmon3haaDckvNn2fBx58ShIJganbe7rsuViZsX87I9xO+gwCFJ5MtPKadnSjZqPoDOYoiRDd0NXcbOEVcnv8G1mxE1OoUknhx7yZwBkwC0MF7NfVcL+Ys6Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741082560; c=relaxed/simple; bh=hY1vWYRwPgCvMe1QGLaM9IUuuNEez24H64MwjGeL+7Q=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=CaL7K9BPfLqhvR2Sb52cjd/7Xz+E7l5jVSp876cqHp8BevQTUKuz7fsZX9YA9jqyZwaHWpoh7AlIkJ4cGaIbCkn5EwBZ+OXDVvMI5nEAuLuSc3k8SWxAxUBLOe1Ag/aAyhxBr5OQueAvsgUnFIB7qhc9aIwsJHRpysiaL+rgdFQ= 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 25F28FEC; Tue, 4 Mar 2025 02:02:51 -0800 (PST) Received: from bogus (e133711.arm.com [10.1.196.55]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2C0923F5A1; Tue, 4 Mar 2025 02:02:33 -0800 (PST) Date: Tue, 4 Mar 2025 10:02:30 +0000 From: Sudeep Holla To: Pierre Gondois Cc: Yicong Yang , , Sudeep Holla , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v11 3/4] arm64: topology: Support SMT control on ACPI based system Message-ID: 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> <2fdea4f6-db98-4dc7-947f-e19ee54d2c3c@arm.com> 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: <2fdea4f6-db98-4dc7-947f-e19ee54d2c3c@arm.com> On Tue, Mar 04, 2025 at 09:25:02AM +0100, Pierre Gondois wrote: > > > 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. Right, but as per Dietmar's and my previous response, it may be a valid case. See latest response from Dietmar which is explicitly requesting support for this. It may need some special handling if we decide to support that. -- Regards, Sudeep