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 20406C021B8 for ; Tue, 4 Mar 2025 10:03:11 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4Z6WTT4rKgz3bkP; Tue, 4 Mar 2025 21:03:09 +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=1741082589; cv=none; b=Bpg+DOuSUAO5kcjaKInHNV9Bu2YhwSGeMQwxvR51IDm6M1Vd4lE7dC/+hJ0mBCPiGdHmEFyHb4CZpCY/72RfStLMMLdpbQ84Bah1Uv8skEWBsqoTo9Eb/aaxQqcOcgnMuoJ7RPfh4iyCJr6ursSdCbDZDuOWDcW/q/DZ7Qntt9PbWT65GTxYTzpsr5wUVhHZocl8CK5YPIuAHAxSh8JrNuWu27do3J9Ky71xekhh21t4EXVg7HzuueVFztOJRZM5tTwslltAOcdTMIVnPCo8mTC+C3piYEmW7gko6Exb2mCvpMj/+fPQG+XeerFzIUCHNXCfnoKdftNRTsBD+xGDmg== ARC-Message-Signature: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1741082589; c=relaxed/relaxed; bh=QTH1Bq/PxKSr1gUXalyKFsKG5IYts2vm06lCPnwHDEY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=dsZTZVtjarMqOFlZpI9Zq/HSRIKktIaPTts9JRCDWg474ndXVHrrhWZm/E1OPd4gbMuPSUfK3qk+rsXeUJ/iAio/3bCZwlIyprurnJvZ14TTwB8+vehr2n2Ba86piDGswCF4B1xpIKZtZbsIxxnHXR2QiHKkLQ+T3RUjQIURxOAU36XaUChtL0/9+WHa2iGoP8bOdEzuA786pi5AgIenhCGgYF9PKpTMKdcOQIM6eKl/kih1BOuE+ORaw3EyKMk33tMsJOiWdiSJcoE1tUR1EL5w8HfxlZ/iZ7+J05uM4pgSwK+6aKocdHB4ExdmJeAZI4RasFKe5gZFf9e4lNqwVA== 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=sudeep.holla@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=sudeep.holla@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 4Z6WTS6R0lz2xdL for ; Tue, 4 Mar 2025 21:03:08 +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 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> 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 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