On Fri, Feb 28, 2025 at 06:51:16PM +0100, Pierre Gondois wrote: > > > On 2/28/25 14:56, Sudeep Holla wrote: > > On Tue, Feb 18, 2025 at 10:10:17PM +0800, Yicong Yang wrote: > > > From: Yicong Yang <yangyic...@hisilicon.com> > > > > > > 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 <jonathan.came...@huawei.com> > > > Signed-off-by: Yicong Yang <yangyic...@hisilicon.com> > > > --- > > > 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 <linux/arch_topology.h> > > > #include <linux/cacheinfo.h> > > > #include <linux/cpufreq.h> > > > +#include <linux/cpu_smt.h> > > > #include <linux/init.h> > > > #include <linux/percpu.h> > > > +#include <linux/xarray.h> > > > #include <asm/cpu.h> > > > #include <asm/cputype.h> > > > @@ -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. > > > > 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. -- Regards, Sudeep
