On 2024/10/24 16:44, Pierre Gondois wrote: > Hello Yicong, > > On 10/15/24 04:18, 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. > > Is it possible to also state that the logic only work for PPTT versions > prior to 6.2. Otherwise find_acpi_cpu_topology_hetero_id() will return > the id of the root node of the PPTT, and all the CPUs of the platform > will be assumed to be identical. >
sure. of course. >> >> 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> >> --- >> arch/arm64/kernel/topology.c | 61 ++++++++++++++++++++++++++++++++++++ >> 1 file changed, 61 insertions(+) >> >> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c >> index 1a2c72f3e7f8..2fa584b932ee 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 +39,29 @@ static bool __init acpi_cpu_is_threaded(int cpu) >> return !!is_threaded; >> } >> +struct cpu_smt_info { >> + int thread_num; >> + int core_id; >> + int cpu; > > It doesn't seem that the 'cpu' is used. Maybe this should be removed, > or used in the error message (I think this could be removed). > sure. will remove.. >> +}; >> + >> /* >> * 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 +71,30 @@ 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; >> + >> + /* >> + * Build up the XArray using the heterogeneous ID of >> + * the CPU cluster. Store the CPU and SMT information >> + * of the first appeared CPU in the CPU cluster of this >> + * heterogeneous ID since the SMT information should be >> + * the same in this CPU cluster. Then we can know the >> + * SMT information of each heterogeneous CPUs in the >> + * system. >> + */ > > A suggestion just in case: > /* > * 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. > * > * One entry is created for each node having: > * - the 'identical implementation' flag > * - its parent not having the flag > */ > ok maybe we can also refer to the comments of find_acpi_cpu_topology_hetero_id() [1] to lead reader there if they want more details. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/acpi/pptt.c#n794 > >> + hetero_id = find_acpi_cpu_topology_hetero_id(cpu); >> + entry = (struct cpu_smt_info *)xa_load(&hetero_cpu, hetero_id); >> + if (!entry) { >> + entry = kzalloc(sizeof(*entry), GFP_KERNEL); >> + WARN_ON(!entry); >> + >> + entry->cpu = cpu; >> + 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 +105,29 @@ 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. >> + */ > > I think it should be ok to remove the above/below comments > I'd leave the above comment since this won't make people who are awared of the efficiency feel nervous about the loop here... will drop the below comment. >> + xa_for_each(&hetero_cpu, hetero_id, entry) { >> + /* >> + * 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 (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; >> + >> + xa_erase(&hetero_cpu, hetero_id); >> + kfree(entry); >> + } >> + >> + cpu_smt_set_num_threads(max_smt_thread_num, max_smt_thread_num); >> + xa_destroy(&hetero_cpu); >> return 0; >> } >> #endif > > Otherwise I tested the SMT detection and it worked well > appreciated for the tests! Thanks.
