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 59FEFC282C6 for ; Mon, 3 Mar 2025 12:09:26 +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=ym2vB8taCXVhXuUVrfzAT1jmbvDb6jkdVJy/SrgbKTc=; b=1m47427UprTsmx4GHcHmah7p2y JKUbRf+OYlGgwcnBXla6/4rk4UAUcUx/Tp7qSQLKG+Ci217KRqqDWi9NRGhu4u5KK0RGcr70iZxC5 W/3y4Nr+9PDW5oGX/4+YHq2Mi0xaPdN1Yic91KpashH1wqBtz+fD55Tx53Q2x4GU+vVHBY6D/0Xre dXsBegaURma9h0T2FSWdZLQPxvIpeQM+XcGl0WmEVuJ4/c3iUPrsZbrz4beQ98rVdcfSBnl0pjcKM zvgfJGhBVY7fYM+InXNJYQJxX6drwRFeTW8Xxjd8Aup9h6GeT0zJ961nhagP+94eEANMty5rJUIge 1ks1FGuQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tp4bj-00000000guK-3rv1; Mon, 03 Mar 2025 12:09:15 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tp3mk-00000000VSq-1eRy for linux-arm-kernel@lists.infradead.org; Mon, 03 Mar 2025 11:16:35 +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 5FC8E113E; Mon, 3 Mar 2025 03:16:45 -0800 (PST) Received: from bogus (e133711.arm.com [10.1.196.55]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0CDCF3F673; Mon, 3 Mar 2025 03:16:26 -0800 (PST) Date: Mon, 3 Mar 2025 11:16:24 +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> 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-20250303_031634_473326_FB739891 X-CRM114-Status: GOOD ( 22.92 ) 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 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 assume entry->thread_num must be set to 1 on single threaded cores Won't that work ? Am I missing something still ? -- Regards, Sudeep