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 0855926D5D1 for ; Fri, 28 Feb 2025 13:56:40 +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=1740751002; cv=none; b=X0PeG4vcck6isNOBEe2foO7Rc+LZDam790nvYMCTTwcLTlZFOR3pr93OXRX/1WELqMTA2nOiOyNta0dRWSHk2+eQBwsA+/sSSlTsXoIMWKGIIdl3s8y+w3WGMFdw0eQEgl0e9HgrUzEP5FoiY/q7DwriJRotH9TE7eEGss9XzU0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740751002; c=relaxed/simple; bh=PAFoTEkrr8GmNmiFdBL3PgCkLKsF919x9Xs8oCWCWLM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=oJcFcKW1z8RbCr4ER+nA5piYg9cFKV0z4DYmz7KoIbY4U/cLjI2Tt7IB40AH62bln3Y3gMaDYhqbnTAQtU2T7PNH7ZAs18x25NV+iRw7csDpUmPJudxECHhY4ijGGoPd5rhAo14hbY7D/RfMnOZ2FPOGxgoNLbJk6uqozd91/5s= 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 6D7221515; Fri, 28 Feb 2025 05:56:55 -0800 (PST) Received: from bogus (e133711.arm.com [10.1.196.55]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0A3B73F6A8; Fri, 28 Feb 2025 05:56:35 -0800 (PST) Date: Fri, 28 Feb 2025 13:56:33 +0000 From: Sudeep Holla To: Yicong Yang Cc: , , , , , 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> 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: <20250218141018.18082-4-yangyicong@huawei.com> On Tue, Feb 18, 2025 at 10:10:17PM +0800, Yicong Yang wrote: > From: Yicong Yang > > For ACPI we'll build the topology from PPTT and we cannot directly > get the SMT number of each core. Instead using a temporary xarray > to record the heterogeneous information (from ACPI_PPTT_ACPI_IDENTICAL) > and SMT information of the first core in its heterogeneous CPU cluster > when building the topology. Then we can know the largest SMT number > in the system. If a homogeneous system's using ACPI 6.2 or later, > all the CPUs should be under the root node of PPTT. There'll be > only one entry in the xarray and all the CPUs in the system will > be assumed identical. > > 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 > > Reviewed-by: Jonathan Cameron > Signed-off-by: Yicong Yang > --- > arch/arm64/kernel/topology.c | 66 ++++++++++++++++++++++++++++++++++++ > 1 file changed, 66 insertions(+) > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > index 1a2c72f3e7f8..6eba1ac091ee 100644 > --- a/arch/arm64/kernel/topology.c > +++ b/arch/arm64/kernel/topology.c > @@ -15,8 +15,10 @@ > #include > #include > #include > +#include > #include > #include > +#include > > #include > #include > @@ -37,17 +39,28 @@ static bool __init acpi_cpu_is_threaded(int cpu) > return !!is_threaded; > } > > +struct cpu_smt_info { > + unsigned int thread_num; > + int core_id; > +}; > + > /* > * Propagate the topology information of the processor_topology_node tree to the > * cpu_topology array. > */ > int __init parse_acpi_topology(void) > { > + unsigned int max_smt_thread_num = 0; > + struct cpu_smt_info *entry; > + struct xarray hetero_cpu; > + unsigned long hetero_id; > int cpu, topology_id; > > if (acpi_disabled) > return 0; > > + xa_init(&hetero_cpu); > + > for_each_possible_cpu(cpu) { > topology_id = find_acpi_cpu_topology(cpu, 0); > if (topology_id < 0) > @@ -57,6 +70,34 @@ int __init parse_acpi_topology(void) > cpu_topology[cpu].thread_id = topology_id; > topology_id = find_acpi_cpu_topology(cpu, 1); > cpu_topology[cpu].core_id = topology_id; > + > + /* > + * In the PPTT, CPUs below a node with the 'identical > + * implementation' flag have the same number of threads. > + * Count the number of threads for only one CPU (i.e. > + * one core_id) among those with the same hetero_id. > + * See the comment of find_acpi_cpu_topology_hetero_id() > + * for more details. > + * > + * One entry is created for each node having: > + * - the 'identical implementation' flag > + * - its parent not having the flag > + */ > + hetero_id = find_acpi_cpu_topology_hetero_id(cpu); > + entry = xa_load(&hetero_cpu, hetero_id); > + if (!entry) { > + entry = kzalloc(sizeof(*entry), GFP_KERNEL); > + WARN_ON_ONCE(!entry); > + > + if (entry) { > + entry->core_id = topology_id; > + entry->thread_num = 1; > + xa_store(&hetero_cpu, hetero_id, > + entry, GFP_KERNEL); > + } > + } else if (entry->core_id == topology_id) { > + entry->thread_num++; > + } > } else { > cpu_topology[cpu].thread_id = -1; > cpu_topology[cpu].core_id = topology_id; > @@ -67,6 +108,31 @@ int __init parse_acpi_topology(void) > cpu_topology[cpu].package_id = topology_id; > } > > + /* > + * This should be a short loop depending on the number of heterogeneous > + * CPU clusters. Typically on a homogeneous system there's only one > + * entry in the XArray. > + */ > + xa_for_each(&hetero_cpu, hetero_id, entry) { > + if (entry->thread_num != max_smt_thread_num && max_smt_thread_num) > + pr_warn_once("Heterogeneous SMT topology is partly supported by SMT control\n"); Ditto as previous patch about handling no threaded cores with threaded cores in the system. I am not sure if that is required but just raising it here. > + > + max_smt_thread_num = max(max_smt_thread_num, entry->thread_num); > + xa_erase(&hetero_cpu, hetero_id); > + kfree(entry); > + } > + > + /* > + * Notify the CPU framework of the SMT support. Initialize the > + * max_smt_thread_num to 1 if no SMT support detected. 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) > + max_smt_thread_num = 1; > + Ditto as previous patch, can get rid if it is default 1. -- Regards, Sudeep