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 5C006C282C6 for ; Fri, 28 Feb 2025 13:58:32 +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=KXYQggls7iQ/CGxbgV/nuZrfJBX6N+DsglBC9T4cwg4=; b=TDMlJPaKFZi4M9pR4DJujYNJZU F4bqTFCgqnJkj1drw5NCmIkiEl/Qv8XbvIDXkZplyB3MTjmqJNKhilYoaJgGwAC2RvRjmJs9Vwvd+ GzjdgS4owCmx8H5xmsgdIf5zARPuy8B0q7vTxquXY7VWtto05nTajBUymyeY4cWwX+gfgXrU+bBQg ZEnVllPDKboaCGeDqgEly8KbosZaR9iyt5CyrEhKLabvk0nntXFGvZyMTWs53/tFK5fWjlHvc0U2N fdnxfS5bpco2RxxI634eO9Vb14pzqw9TFgDsuIaDTINxgXZrmsiyUQCwZuSxVEGNnGYcVMqQ+Y5ZL gw1J8RLg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1to0si-0000000B9j9-1sWP; Fri, 28 Feb 2025 13:58:24 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1to0p2-0000000B927-2vLs for linux-arm-kernel@lists.infradead.org; Fri, 28 Feb 2025 13:54:38 +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 4DACD1688; Fri, 28 Feb 2025 05:54:51 -0800 (PST) Received: from bogus (e133711.arm.com [10.1.196.55]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DF7283F6A8; Fri, 28 Feb 2025 05:54:31 -0800 (PST) Date: Fri, 28 Feb 2025 13:54:29 +0000 From: Sudeep Holla To: Yicong Yang Cc: , , , Sudeep Holla , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v11 2/4] arch_topology: Support SMT control for OF based system Message-ID: References: <20250218141018.18082-1-yangyicong@huawei.com> <20250218141018.18082-3-yangyicong@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250218141018.18082-3-yangyicong@huawei.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250228_055436_825112_70F24C5D X-CRM114-Status: GOOD ( 29.22 ) 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, Feb 18, 2025 at 10:10:16PM +0800, Yicong Yang wrote: > From: Yicong Yang > > On building the topology from the devicetree, we've already > gotten the SMT thread number of each core. Update the largest > SMT thread number and enable the SMT control by the end of > topology parsing. > > The core's SMT control provides two interface to the users [1]: > 1) enable/disable SMT by writing on/off > 2) enable/disable SMT by writing thread number 1/max_thread_number > > If a system have more than one SMT thread number the 2) may > not handle it well, since there're multiple thread numbers in the > system and 2) only accept 1/max_thread_number. So issue a warning > to notify the users if such system detected. > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/testing/sysfs-devices-system-cpu#n542 > > Signed-off-by: Yicong Yang > --- > drivers/base/arch_topology.c | 27 +++++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c > index 3ebe77566788..23f425a9d77a 100644 > --- a/drivers/base/arch_topology.c > +++ b/drivers/base/arch_topology.c > @@ -11,6 +11,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -506,6 +507,10 @@ core_initcall(free_raw_capacity); > #endif > > #if defined(CONFIG_ARM64) || defined(CONFIG_RISCV) > + > +/* Maximum SMT thread number detected used to enable the SMT control */ > +static unsigned int max_smt_thread_num; > + > /* > * This function returns the logic cpu number of the node. > * There are basically three kinds of return values: > @@ -565,6 +570,16 @@ static int __init parse_core(struct device_node *core, int package_id, > i++; > } while (1); > > + /* > + * If max_smt_thread_num has been initialized and doesn't match > + * the thread number of this entry, then the system has > + * heterogeneous SMT topology. > + */ > + if (max_smt_thread_num && max_smt_thread_num != i) > + pr_warn_once("Heterogeneous SMT topology is partly supported by SMT control\n"); > + May be we need to make it more conditional as we may have to support systems with few cores that are single threaded ? I think Dietmar's comment is about that. > + max_smt_thread_num = max_t(unsigned int, max_smt_thread_num, i); > + > cpu = get_cpu_for_node(core); > if (cpu >= 0) { > if (!leaf) { > @@ -677,6 +692,18 @@ static int __init parse_socket(struct device_node *socket) > if (!has_socket) > ret = parse_cluster(socket, 0, -1, 0); > > + /* > + * Notify the CPU framework of the SMT support. Initialize the > + * max_smt_thread_num to 1 if no SMT support detected or failed > + * to parse the topology. A thread number of 1 can be handled by > + * the framework so we don't need to check max_smt_thread_num to > + * see we support SMT or not. > + */ > + if (!max_smt_thread_num || ret) > + max_smt_thread_num = 1; > + For the failed parsing of topology, reset_cpu_topology() gets called. I suggest resetting max_smt_thread_num to 1 belongs there. And if you start with max_smt_thread_num, we don't need to update it to 1 explicitly here. So I would like to get rid of above check completely. -- Regards, Sudeep