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 1D818C282D0 for ; Tue, 4 Mar 2025 10:35:40 +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=QTH1Bq/PxKSr1gUXalyKFsKG5IYts2vm06lCPnwHDEY=; b=ny5WhbduLoi3WOvs8i/04/5Knt YH3oHj0fOlWFXQDMXMWZZN1+wzBN5/dDTIuyd/MeTYyVM5VfEfvU34/kAmfUiB4K356a3WgP4bnnT mMWpBUdZJnG9eNzCkNGt1mGcf+tYZ8w8i1tjB8r2VBV2vxujskkZApaIeHwzHOdVSqzCzcM0ONBpC Kr2mTMk3TwfxxQPJvpRl8On6opVeIKiXmWLgqyhyqQaqo+4lmKnI7jS6SEKCFNDCCqghHu4sKoCiO +ltQ6dDDOCfsbzDX9FvZXpZbMATzJ+5jj95bozPKTAyFEubznLY/2B8mn+W4hCCnQiUcoj92M3Ndx 8gfzAjnw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tpPcY-00000004Asj-1hxG; Tue, 04 Mar 2025 10:35:30 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tpP6k-000000043RJ-050j for linux-arm-kernel@lists.infradead.org; Tue, 04 Mar 2025 10:02:39 +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 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2fdea4f6-db98-4dc7-947f-e19ee54d2c3c@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250304_020238_149845_2CF44D28 X-CRM114-Status: GOOD ( 30.48 ) 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 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