【记录一个问题】android ndk下设置线程的亲缘性，总有两个核无法设置成功

参考了这篇文章：https://blog.csdn.net/lanyzh0909/article/details/50404664
大体的代码如下：

#include <pthread.h>
#include <sched.h>

#include <stdio.h>
#include <stdlib.h>
#include <sys/sysinfo.h>
#include <sys/types.h>
#include <unistd.h>

void* _thread_func(void* param){
    int thread_index = *(int*)param;
    int cpu_count = sysconf(_SC_NPROCESSORS_CONF);
    cpu_set_t mask;                // CPU核的集合
    cpu_set_t get;                 //获取在集合中的CPU
    CPU_ZERO(&mask);               //置空
    CPU_SET(thread_index, &mask);  //设置亲和力值
    //设置线程CPU亲和力
    if (sched_setaffinity(0, sizeof(mask), &mask) == -1) {
      printf("warning: could not set CPU %d affinity, continuing...
", thread_index);
    } else {
      printf("thread %d set to cpu %d
", thread_index, thread_index);
    }    
}

在高通骁龙835处理器上，始终打印如下内容：
warning: could not set CPU 7 affinity, continuing...
thread 1 set to cpu 1
thread 0 set to cpu 0
thread 3 set to cpu 3
thread 2 set to cpu 2
warning: could not set CPU 4 affinity, continuing...
thread 5 set to cpu 5
thread 6 set to cpu 6

猜测是系统故意让其中的两个核无法被设置亲缘性，原因未知。