On Fri, 20 Dec 2024 15:53:12 +0800 Yicong Yang <yangyic...@huawei.com> 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 > Signed-off-by: Yicong Yang <yangyic...@hisilicon.com> A few trivial things inline. Either way it's fine as really just my style preferences Reviewed-by: Jonathan Cameron <jonathan.came...@huawei.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..85cb18d72a29 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 { > + 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) > { > + 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 +70,32 @@ 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 = (struct cpu_smt_info *)xa_load(&hetero_cpu, > hetero_id); Given xa_load returns a void *, entry = xa_load(&hetero_cpu, hetero_id); should be fine (I haven't checked local style, so feel free to ignore if local style is to cast anyway). Maybe drag the definition of entry into a more local scope as well. > + if (!entry) { > + entry = kzalloc(sizeof(*entry), GFP_KERNEL); > + WARN_ON(!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 +106,33 @@ 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"); > + > + if (entry->thread_num > max_smt_thread_num) > + max_smt_thread_num = entry->thread_num; As with DT, maybe min is more informative? max_smt_thread_num = min(max_smt_thread_num, entry->thread_num); I don't care strongly about it though. > + > + 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; > + > + cpu_smt_set_num_threads(max_smt_thread_num, max_smt_thread_num); > + xa_destroy(&hetero_cpu); > return 0; > } > #endif
