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Question

Android bionic defines a series of structs that are used specifically to handle kernel level uapi data, like sysinfo.h header which defines a struct called sysinfo that defines registers for kernel "ram" uapi in an easy way, like when using sysinfo.totalram we can get a totalram from device, but i need a thing like this but for numbers of cpu cores and if are possible number of cpu threads, someone knows a struct that defines it?

bionic/libc/kernel/uapi/linux

struct that defines number of cpu cores

Answer 1

To be honest, it's so hard to dig into the kernel that I only found the way to get it in C++. Hopes that may help.

• cpu cores

Runtime.availableProcessors();

public int availableProcessors() {
  return (int) Libcore.os.sysconf(_SC_NPROCESSORS_CONF);
}

You can reference the source code from sysinfo.cpp.

int __get_cpu_count(const char* sys_file) {
  int cpu_count = 1;
  FILE* fp = fopen(sys_file, "re");
  if (fp != nullptr) {
    char* line = nullptr;
    size_t allocated_size = 0;
    if (getline(&line, &allocated_size, fp) != -1) {
      cpu_count = GetCpuCountFromString(line);
    }
    free(line);
    fclose(fp);
  }
  return cpu_count;
}

int get_nprocs_conf() {
  // It's unclear to me whether this is intended to be "possible" or "present",
  // but on mobile they're unlikely to differ.
  return __get_cpu_count("/sys/devices/system/cpu/possible");
}

int get_nprocs() {
  return __get_cpu_count("/sys/devices/system/cpu/online");
}

• cpu threads

Also sees cpustats.c.

/*
 * Get the number of CPUs of the system.
 *
 * Uses the two files /sys/devices/system/cpu/present and
 * /sys/devices/system/cpu/online to determine the number of CPUs. Expects the
 * format of both files to be either 0 or 0-N where N+1 is the number of CPUs.
 *
 * Exits if the present CPUs is not equal to the online CPUs
 */
static int get_cpu_count() {
    int cpu_count = get_cpu_count_from_file("/sys/devices/system/cpu/present");
    if (cpu_count != get_cpu_count_from_file("/sys/devices/system/cpu/online")) {
        die("present cpus != online cpus\n");
    }
    return cpu_count;
}

/*
 * Get the number of CPUs from a given filename.
 */
static int get_cpu_count_from_file(char* filename) {
    FILE* file;
    char line[MAX_BUF_SIZE];
    int cpu_count;

    file = fopen(filename, "r");
    if (!file) die("Could not open %s\n", filename);
    if (!fgets(line, MAX_BUF_SIZE, file)) die("Could not get %s contents\n", filename);
    fclose(file);

    if (strcmp(line, "0\n") == 0) {
        return 1;
    }

    if (1 == sscanf(line, "0-%d\n", &cpu_count)) {
        return cpu_count + 1;
    }

    die("Unexpected input in file %s (%s).\n", filename, line);
    return -1;
}