一．CPU affinity
linux中将某个进程或者线程绑定到特定的一个或者多个cpu上执行。
二．为什么需要CPU affinity
cache性能的提升，多个进程不断交替地在某个cpu上执行，导致缓存无效。
多线程程序运行于某个cpu，每个线程轮流占据cpu资源，共享cache，导致cache性能下降。
专有程序的实时性，当把专有进程保定与一个核，其余所有进程绑定与剩余的核，保证了专有程序的性能。
三．Linux cpu affinity 调用函数
a．进程cpu affinity设置
int sched_setaffinity(pid_t pid, size_t cpusetsize, cpu_set_t *mask);
int sched_getaffinity(pid_t pid, size_t cpusetsize, cpu_set_t *mask);
第一个函数设置进程号为pid的cpu亲和性
第二个函数获取进程号为pid的cpu亲和性
b.线程cpu affinity设置
int pthread_setaffinity_np(pthread_t thread, size_t cpusetsize, onst cpu_set_t *cpuset);
int pthread_getaffinity_np(pthread_t thread, size_t cpusetsize, cpu_set_t *cpuset);
第一个函数设置线程号为thread的cpu 亲和性
第二个函数获取线程号为thread的cpu 亲和性
四．例子
1. 进程cpu affinity设置 task_affi.c:
#define _GNU_SOURCE
#include <stdio.h>
#include <math.h>
#include <unistd.h>
#include <sched.h>
#include <pthread.h>
#include <assert.h>
/*waste some time but ,ocuppy the cup*/
static waste_time(long n)
{
double res = 0;
long i = 0;
while(i <n * 200000) {
i++;
res += sqrt(i);
}
return res;
}
int main()
{
cpu_set_t cpuset;
int ret, j, num_cpus, core;
pid_t pid;
pid = getpid();
num_cpus = sysconf(_SC_NPROCESSORS_CONF);/*get the cpu nums*/
assert(num_cpus > 0);
printf("cpu num:%d\n", num_cpus);
core = 0 % num_cpus;
CPU_ZERO(&cpuset);
CPU_SET(core, &cpuset);
ret = sched_setaffinity(pid, sizeof(cpu_set_t), &cpuset);
assert(ret == 0);
ret = sched_getaffinity(pid, sizeof(cpu_set_t), &cpuset);
assert(ret == 0);
for (j = 0; j < CPU_SETSIZE; j++)
if (CPU_ISSET(j, &cpuset))
printf("after set program bind on CPU %d\n", j);
printf ("core %d result: %f\n", core, waste_time (5000));
core = 1%num_cpus;
CPU_ZERO(&cpuset);
CPU_SET(core, &cpuset);
ret = sched_setaffinity(pid, sizeof(cpu_set_t), &cpuset);
assert(ret == 0);
ret = sched_getaffinity(pid, sizeof(cpu_set_t), &cpuset);
assert(ret == 0);
for (j = 0; j < CPU_SETSIZE; j++)
if (CPU_ISSET(j, &cpuset))
printf("after set program bind on CPU %d\n", j);
printf ("core %d result: %f\n", core, waste_time (5000));
return 0;
}
gcc 编译：
gcc task_affi.c -lm
2. 线程cpu affinity设置 thread_affi.c：
#define _GNU_SOURCE
#include <stdio.h>
#include <unistd.h>
#include <sched.h>
#include <pthread.h>
#include <assert.h>
static int cpu_nums;
static waste_time(long n)
{
double res = 0;
long i = 0;
while(i <n * 200000) {
i++;
res += sqrt(i);
}
return res;
}
void *function1(void *argc)
{
pthread_t thread_id;
int ret, j, core;
cpu_set_t cpuset;
thread_id = pthread_self();
printf("porgran pid:%u, the function1 pthread id is %lu\n",getpid(), thread_id);
core = 0 % cpu_nums;
CPU_ZERO(&cpuset);
CPU_SET(core, &cpuset);
ret = pthread_setaffinity_np(thread_id, sizeof(cpu_set_t), &cpuset);
assert(ret == 0);
/* Check the actual affinity mask assigned to the thread */
ret = pthread_getaffinity_np(thread_id, sizeof(cpu_set_t), &cpuset);
assert(ret == 0);
printf("thread_id:%lu set the cpu:", thread_id);
for (j = 0; j < CPU_SETSIZE; j++)
if (CPU_ISSET(j, &cpuset))
printf(" CPU %d\n\n", j);
printf ("the function1 pthread id is %lu, bind core %d \n", thread_id, core );
printf("the function1 result: %f \n\n",waste_time (5000) );
return 0;
}
void *function2(void *argc)
{
pthread_t thread_id;
int ret, j, core;
cpu_set_t cpuset;
thread_id = pthread_self();
printf("porgran pid:%u, the function2 pthread id is %lu\n",getpid(), thread_id);
sleep(5);
core = 1 % cpu_nums;
CPU_ZERO(&cpuset);
CPU_SET(core, &cpuset);
ret = pthread_setaffinity_np(thread_id, sizeof(cpu_set_t), &cpuset);
assert(ret == 0);
/* Check the actual affinity mask assigned to the thread */
ret = pthread_getaffinity_np(thread_id, sizeof(cpu_set_t), &cpuset);
assert(ret == 0);
printf("thread_id:%lu set the cup:\n", thread_id);
for (j = 0; j < CPU_SETSIZE; j++)
if (CPU_ISSET(j, &cpuset))
printf(" CPU %d\n", j);
printf ("the function2 pthread id is %lu, bind core %d \n", thread_id, core);
printf ("the function2 result is: %f\n",waste_time (5000) );
return 0;
}
int main()
{
pthread_t thread_id[2];
int ret, j, core;
pthread_t main_thread_id;
cpu_set_t cpuset;
main_thread_id = pthread_self();
cpu_nums = sysconf(_SC_NPROCESSORS_CONF);
assert(cpu_nums > 0);
printf("cpu num:%d\n", cpu_nums);
core = 0 % cpu_nums;
printf("porgran pid:%u, mian_thread_id:%lu\n", getpid(), main_thread_id);
ret = pthread_create(thread_id, NULL, function1, NULL);
assert(ret == 0);
ret = pthread_create(thread_id + 1, NULL, function2, NULL);
assert(ret == 0);
ret = pthread_join(thread_id[0], NULL);
assert(ret == 0);
ret = pthread_join(thread_id[1], NULL);
assert(ret == 0);
core = 2 % cpu_nums;
CPU_ZERO(&cpuset);
CPU_SET(core, &cpuset);
ret = pthread_setaffinity_np(main_thread_id, sizeof(cpu_set_t), &cpuset);
assert(ret == 0);
/* Check the actual affinity mask assigned to the thread */
ret = pthread_getaffinity_np(main_thread_id, sizeof(cpu_set_t), &cpuset);
assert(ret == 0);
printf("mian_thread_id:%lu set the cpu:", main_thread_id);
for (j = 0; j < CPU_SETSIZE; j++)
if (CPU_ISSET(j, &cpuset))
printf(" CPU %d \n\n", j);
printf ("the main function pthread id is %lu, bind core %d result: %f\n", main_thread_id, core, waste_time (5000));
return 0;
}
gcc 编译：
$ gcc thread_affi.c -lpthread -lm
执行程序时可以通过top命令，然后按‘1’，查看各个cpu的使用情况.