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 0DA72187550 for ; Mon, 3 Mar 2025 11:16:31 +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=1741000594; cv=none; b=EYHmzW7oUOfWHtE8opK0wjrBjinI7/x5u03RuyPjBqBufaAsZK/4HPF7VNMof3eMPie4U1PVINT1lf7iZXhN9LlX9+THBDJFxtvj6jF7oNlUoNCoFuEds+3VO2TvBtQWAJ5ZrDcXWzayhRTZv3zsN+jzIPVGFhsSSSoR9JjJDIQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741000594; c=relaxed/simple; bh=0QHtPaQ98QlNVRE7GqZcnxV1R2pOH0/NOPZdOvOZ7Wo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=J6grjwYgQmSNB9wRiAmaFjcrZ/En/W2cxIwodrVdzV0F79IwOUjfsSIqyq6RFikaTbXk3Ugd37VBfkqhIjIUMsuxVfEwi3/5rST9cw3cPkEpO2ggpE718rATNM2AAS9cXlRo1G75i6Ii61c7hEFSIavy164wOJinTGtA5K3SszU= 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 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> 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: 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