Linux中CPU亲和性

Linux中CPU亲和性

超线程技术(Hyper-Threading)：就是利用特殊的硬件指令，把两个逻辑内核(CPU core)模拟成两个物理芯片，让单个处理器都能使用线程级并行计算，进而兼容多线程操作系统和软件，减少了CPU的闲置时间，提高的CPU的运行效率。我们常听到的双核四线程/四核八线程指的就是支持超线程技术的CPU

物理CPU:机器上安装的实际CPU, 比如说你的主板上安装了一个8核CPU,那么物理CPU个数就是1个,所以物理CPU个数就是主板上安装的CPU个数

逻辑CPU:一般情况，我们认为一颗CPU可以有多核，加上intel的超线程技术(HT), 可以在逻辑上再分一倍数量的CPU core出来

绑定任务到特定CPU（CPU亲和性）

Linux下查看CPU相关信息, CPU的信息主要都在/proc/cupinfo中

# 查看物理CPU个数
cat /proc/cpuinfo|grep "physical id"|sort -u|wc -l

# 查看每个物理CPU中core的个数(即核数)
cat /proc/cpuinfo|grep "cpu cores"|uniq

# 查看逻辑CPU的个数
cat /proc/cpuinfo|grep "processor"|wc -l

# 查看CPU的名称型号
cat /proc/cpuinfo|grep "name"|cut -f2 -d:|uniq

Linux查看某个进程运行在哪个逻辑CPU上

ps -eo pid,args,psr
#参数的含义：
pid  - 进程ID
args - 该进程执行时传入的命令行参数
psr  - 分配给进程的逻辑CPU

例子:
[~]# ps -eo pid,args,psr | grep nginx
9073 nginx: master process /usr/   1
9074 nginx: worker process         0
9075 nginx: worker process         1
9076 nginx: worker process         2
9077 nginx: worker process         3
13857 grep nginx                   3

Linux查看线程的TID

TID就是Thread ID,他和POSIX中pthread_t表示的线程ID完全不是同一个东西.

Linux中的POSIX线程库实现的线程其实也是一个轻量级进程(LWP),这个TID就是这个线程的真实PID.

但是又不能通过getpid()函数获取，Linux中定义了gettid()这个接口，但是通常都是未实现的，所以需要使用下面的方式获取TID。

//program
#include <sys/syscall.h>  
pid_t tid;
tid = syscall(__NR_gettid);// or syscall(SYS_gettid)  

//command-line 3种方法(推荐第三种方法)
（1）ps -efL | grep prog_name
（2）ls /proc/pid/task            //文件夹名即TID
（3）ps -To 'pid,lwp,psr,cmd' -p PID

基本概念

CPU affinity 是一种调度属性(scheduler property), 它可以将一个进程"绑定" 到一个或一组CPU上.

在SMP(Symmetric Multi-Processing对称多处理)架构下，Linux调度器(scheduler)会根据CPU affinity的设置让指定的进程运行在"绑定"的CPU上,而不会在别的CPU上运行.

Linux调度器同样支持自然CPU亲和性(natural CPU affinity): 调度器会试图保持进程在相同的CPU上运行, 这意味着进程通常不会在处理器之间频繁迁移,进程迁移的频率小就意味着产生的负载小。

因为程序的作者比调度器更了解程序,所以我们可以手动地为其分配CPU核，而不会过多地占用CPU0，或是让我们关键进程和一堆别的进程挤在一起,所有设置CPU亲和性可以使某些程序提高性能。

表示方法

CPU affinity 使用位掩码(bitmask)表示, 每一位都表示一个CPU, 置1表示"绑定".

最低位表示第一个逻辑CPU, 最高位表示最后一个逻辑CPU.

CPU affinity典型的表示方法是使用16进制,具体如下.

0x00000001
    is processor #0

0x00000003
    is processors #0 and #1

0xFFFFFFFF
    is all processors (#0 through #31)

taskset命令

taskset命名用于获取或者设定CPU亲和性

# 命令行形式
taskset [options] mask command [arg]...
taskset [options] -p [mask] pid

PARAMETER
　　　　mask : cpu亲和性,当没有-c选项时, 其值前无论有没有0x标记都是16进制的,
　　　　　　　　当有-c选项时,其值是十进制的.
　　　　command : 命令或者可执行程序
　　　　arg : command的参数
　　　　pid : 进程ID,可以通过ps/top/pidof等命令获取


OPTIONS
　　　　-a, --all-tasks (旧版本中没有这个选项)
　　　　　　　　这个选项涉及到了linux中TID的概念,他会将一个进程中所有的TID都执行一次CPU亲和性设置.
　　　　　　　　TID就是Thread ID,他和POSIX中pthread_t表示的线程ID完全不是同一个东西.
　　　　　　　　Linux中的POSIX线程库实现的线程其实也是一个进程(LWP),这个TID就是这个线程的真实PID.
       -p, --pid
              操作已存在的PID,而不是加载一个新的程序
       -c, --cpu-list
              声明CPU的亲和力使用数字表示而不是用位掩码表示. 例如 0,5,7,9-11.
       -h, --help
              display usage information and exit
       -V, --version
              output version information and exit
  USAGE

　　　　1) 使用指定的CPU亲和性运行一个新程序

　　　　　　taskset [-c] mask command [arg]...

　　　　　　　　举例:使用CPU0运行ls命令显示/etc/init.d下的所有内容 

　　　　　　　　　　taskset -c 0 ls -al /etc/init.d/

　　　　2) 显示已经运行的进程的CPU亲和性

　　　　　　taskset -p pid

　　　　　　　　举例:查看init进程(PID=1)的CPU亲和性

　　　　　　　　　　taskset -p 1

　　　　3) 改变已经运行进程的CPU亲和力

　　　　    taskset -p[c] mask pid

　　　　　　　　举例:打开2个终端,在第一个终端运行top命令,第二个终端中

　　　　　　　　　　首先运行:[~]# ps -eo pid,args,psr | grep top #获取top命令的pid和其所运行的CPU号

　　　　　　　　　　其次运行:[~]# taskset -cp 新的CPU号 pid       #更改top命令运行的CPU号

　　　　　　　　　　最后运行:[~]# ps -eo pid,args,psr | grep top #查看是否更改成功

  PERMISSIONS
        一个用户要设定一个进程的CPU亲和性,如果目标进程是该用户的,则可以设置,如果是其他用户的,则会设置失败,提示 Operation not permitted.当然root用户没有任何限制.

        任何用户都可以获取任意一个进程的CPU亲和性.

编程API

下面是用用于设置和获取CPU亲和性相关的API.

#define _GNU_SOURCE
#include <sched.h>
#include <pthread.h> //for pthread functions(last 4) 注意<pthread.h>包含<sched.h>

/* MACRO */
    /* The following macros are provided to operate on the CPU set set */
        /* Clears set, so that it contains no CPUs */
        void CPU_ZERO(cpu_set_t *set);
        void CPU_ZERO_S(size_t setsize, cpu_set_t *set);
        
        /* Add CPU cpu to set */
        void CPU_SET(int cpu, cpu_set_t *set);
        void CPU_SET_S(int cpu, size_t setsize, cpu_set_t *set);
        
        /* Remove CPU cpu from set */
        void CPU_CLR(int cpu, cpu_set_t *set);
        void CPU_CLR_S(int cpu, size_t setsize, cpu_set_t *set);
        
        /* Test to see if CPU cpu is a member of set */
        int CPU_ISSET(int cpu, cpu_set_t *set);
        int CPU_ISSET_S(int cpu, size_t setsize, cpu_set_t *set);
        
        /* Return the number of CPUs in set */
        void CPU_COUNT(cpu_set_t *set);
        void CPU_COUNT_S(size_t setsize, cpu_set_t *set);
    
    /* The following macros perform logical operations on CPU sets */
        /* Store the logical AND of the sets srcset1 and srcset2 in destset (which may be one of the source sets). */
        void CPU_AND(cpu_set_t *destset, cpu_set_t *srcset1, cpu_set_t *srcset2);
        void CPU_AND_S(size_t setsize, cpu_set_t *destset, cpu_set_t *srcset1, cpu_set_t *srcset2);
        
        /* Store the logical OR of the sets srcset1 and srcset2 in destset (which may be one of the source sets). */
        void CPU_OR(cpu_set_t *destset, cpu_set_t *srcset1, cpu_set_t *srcset2);
        void CPU_OR_S(size_t setsize, cpu_set_t *destset, cpu_set_t *srcset1, cpu_set_t *srcset2);
        
        /* Store  the logical XOR of the sets srcset1 and srcset2 in destset (which may be one of the source sets). */
        void CPU_XOR(cpu_set_t *destset, cpu_set_t *srcset1, cpu_set_t *srcset2);
        void CPU_XOR_S(size_t setsize, cpu_set_t *destset, cpu_set_t *srcset1, cpu_set_t *srcset2);
        
        /* Test whether two CPU set contain exactly the same CPUs. */
        int CPU_EQUAL(cpu_set_t *set1, cpu_set_t *set2);
        int CPU_EQUAL_S(size_t setsize, cpu_set_t *set1, cpu_set_t *set2);
    
    /* The following macros are used to allocate and deallocate CPU sets: */
        /* Allocate a CPU set large enough to hold CPUs in the range 0 to num_cpus-1 */
        cpu_set_t *CPU_ALLOC(int num_cpus);
    
        /* Return the size in bytes of the CPU set that would be needed to  hold  CPUs  in the  range 0 to num_cpus-1. 
           This macro provides the value that can be used for the setsize argument in the CPU_*_S() macros */
        size_t CPU_ALLOC_SIZE(int num_cpus);
        
        /* Free a CPU set previously allocated by CPU_ALLOC(). */
        void CPU_FREE(cpu_set_t *set);

/* API */
    /* Set the CPU affinity for a task */
    int sched_setaffinity(pid_t pid, size_t cpusetsize, cpu_set_t *mask);
    /* Get the CPU affinity for a task */
    int sched_getaffinity(pid_t pid, size_t cpusetsize, cpu_set_t *mask);
    
    /* set CPU affinity attribute in thread attributes object */
    int pthread_attr_setaffinity_np(pthread_attr_t *attr, size_t cpusetsize, const cpu_set_t *cpuset);
    /* get CPU affinity attribute in thread attributes object */
    int pthread_attr_getaffinity_np(const pthread_attr_t *attr, size_t cpusetsize, cpu_set_t *cpuset);
    
    /* set CPU affinity of a thread */
    int pthread_setaffinity_np(pthread_t thread, size_t cpusetsize, const cpu_set_t *cpuset);
    /* get CPU affinity of a thread */
    int pthread_getaffinity_np(pthread_t thread, size_t cpusetsize, cpu_set_t *cpuset);

相关的宏通常都分为2种,一种是带_S后缀的,一种不是不带_S后缀的, 从声明上看带_S后缀的宏都多出一个参数 setsize.

从功能上看他们的区别是带_S后缀的宏是用于操作动态申请的CPU set(s),所谓的动态申请其实就是使用宏 CPU_ALLOC 申请,

参数setsize 可以是通过宏 CPU_ALLOC_SIZE 获得,两者的用法详见下面的例子.

相关的API只有6个, 前2个是用来设置进程的CPU亲和性，需要注意的一点是,当这2个API的第一个参数pid为0时,表示使用调用进程的进程ID；

后4个是用来设置线程的CPU亲和性。其实sched_setaffinity()也可以用来设置线程的CPU的亲和性，也就是taskset “-a”选项中提到的TID概念。

例子一:使用2种方式(带和不带_S后缀的宏)获取当前进程的CPU亲和性

#define _GNU_SOURCE
#include <sched.h>
#include <unistd.h> /* sysconf */
#include <stdlib.h> /* exit */
#include <stdio.h>

int main(void)
{
    int i, nrcpus;
    cpu_set_t mask;
    unsigned long bitmask = 0;
    
    CPU_ZERO(&mask);
    
     /* Get the CPU affinity for a pid */
    if (sched_getaffinity(0, sizeof(cpu_set_t), &mask) == -1) 
    {   
        perror("sched_getaffinity");
        exit(EXIT_FAILURE);
    }
    
       /* get logical cpu number */
    nrcpus = sysconf(_SC_NPROCESSORS_CONF);
    
    for (i = 0; i < nrcpus; i++)
    {
        if (CPU_ISSET(i, &mask))
        {
            bitmask |= (unsigned long)0x01 << i;
            printf("processor #%d is set\n", i); 
        }
    }
    printf("bitmask = %#lx\n", bitmask);

    exit(EXIT_SUCCESS);
}
/*----------------------------------------------------------------*/
#define _GNU_SOURCE
#include <sched.h>
#include <unistd.h> /* sysconf */
#include <stdlib.h> /* exit */
#include <stdio.h>

int main(void)
{
    int i, nrcpus;
    cpu_set_t *pmask;
    size_t cpusize;
    unsigned long bitmask = 0;

    /* get logical cpu number */
    nrcpus = sysconf(_SC_NPROCESSORS_CONF);
    
    pmask = CPU_ALLOC(nrcpus);
    cpusize = CPU_ALLOC_SIZE(nrcpus);
    CPU_ZERO_S(cpusize, pmask);
    
    /* Get the CPU affinity for a pid */
    if (sched_getaffinity(0, cpusize, pmask) == -1) 
    {
        perror("sched_getaffinity");
        CPU_FREE(pmask);
        exit(EXIT_FAILURE);
    }
    for (i = 0; i < nrcpus; i++)
    {
        if (CPU_ISSET_S(i, cpusize, pmask))
        {
             bitmask |= (unsigned long)0x01 << i;
            printf("processor #%d is set\n", i); 
        }
    }
      printf("bitmask = %#lx\n", bitmask);
      
    CPU_FREE(pmask);
    exit(EXIT_SUCCESS);
}

执行结果如下(4核CPU):

[cpu_affinity #1]$ gcc -g -Wall cpu_affinity.c
[cpu_affinity #2]$ taskset 1 ./a.out 
processor #0 is set
bitmask = 0x1
[cpu_affinity #3]$ taskset 1 ./a.out 
processor #0 is set
bitmask = 0x1
[cpu_affinity #4]$ taskset 2 ./a.out 
processor #1 is set
bitmask = 0x2
[cpu_affinity #5]$ taskset 3 ./a.out 
processor #0 is set
processor #1 is set
bitmask = 0x3
[cpu_affinity #6]$ taskset 4 ./a.out 
processor #2 is set
bitmask = 0x4
[cpu_affinity #7]$ taskset 5 ./a.out 
processor #0 is set
processor #2 is set
bitmask = 0x5
[cpu_affinity #8]$ taskset 6 ./a.out 
processor #1 is set
processor #2 is set
bitmask = 0x6
[cpu_affinity #9]$ taskset 7 ./a.out 
processor #0 is set
processor #1 is set
processor #2 is set
bitmask = 0x7
[cpu_affinity #10]$ taskset 8 ./a.out 
processor #3 is set
bitmask = 0x8
[cpu_affinity #11]$ taskset 9 ./a.out 
processor #0 is set
processor #3 is set
bitmask = 0x9
[cpu_affinity #12]$ taskset A ./a.out 
processor #1 is set
processor #3 is set
bitmask = 0xa
[cpu_affinity #13]$ taskset B ./a.out 
processor #0 is set
processor #1 is set
processor #3 is set
bitmask = 0xb
[cpu_affinity #14]$ taskset C ./a.out 
processor #2 is set
processor #3 is set
bitmask = 0xc
[cpu_affinity #15]$ taskset D ./a.out 
processor #0 is set
processor #2 is set
processor #3 is set
bitmask = 0xd
[cpu_affinity #16]$ taskset E ./a.out 
processor #1 is set
processor #2 is set
processor #3 is set
bitmask = 0xe
[cpu_affinity #17]$ taskset F ./a.out 
processor #0 is set
processor #1 is set
processor #2 is set
processor #3 is set
bitmask = 0xf
[cpu_affinity #18]$ taskset 0 ./a.out 
sched_setaffinity: Invalid argument
failed to set pid 0's affinity.

例子二:设置进程的CPU亲和性后再获取显示CPU亲和性

#define _GNU_SOURCE
#include <sched.h>
#include <unistd.h> /* sysconf */
#include <stdlib.h> /* exit */
#include <stdio.h>

int main(void)
{
    int i, nrcpus;
    cpu_set_t mask;
    unsigned long bitmask = 0;
    
    CPU_ZERO(&mask);
    
    CPU_SET(0, &mask); /* add CPU0 to cpu set */
    CPU_SET(2, &mask); /* add CPU2 to cpu set */

      /* Set the CPU affinity for a pid */
    if (sched_setaffinity(0, sizeof(cpu_set_t), &mask) == -1) 
    {   
        perror("sched_setaffinity");
        exit(EXIT_FAILURE);
    }
    
    CPU_ZERO(&mask);
    
     /* Get the CPU affinity for a pid */
    if (sched_getaffinity(0, sizeof(cpu_set_t), &mask) == -1) 
    {   
        perror("sched_getaffinity");
        exit(EXIT_FAILURE);
    }

       /* get logical cpu number */
    nrcpus = sysconf(_SC_NPROCESSORS_CONF);
    
    for (i = 0; i < nrcpus; i++)
    {
        if (CPU_ISSET(i, &mask))
        {
            bitmask |= (unsigned long)0x01 << i;
            printf("processor #%d is set\n", i); 
        }
    }
    printf("bitmask = %#lx\n", bitmask);

    exit(EXIT_SUCCESS);
}

例子三：设置线程的CPU属性后再获取显示CPU亲和性

这个例子来源于Linux的man page.

#define _GNU_SOURCE
#include <pthread.h> //不用再包含<sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

#define handle_error_en(en, msg) \
        do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)

int
main(int argc, char *argv[])
{
    int s, j;
    cpu_set_t cpuset;
    pthread_t thread;
    
    thread = pthread_self();
    
    /* Set affinity mask to include CPUs 0 to 7 */
    CPU_ZERO(&cpuset);
    for (j = 0; j < 8; j++)
        CPU_SET(j, &cpuset);
    
    s = pthread_setaffinity_np(thread, sizeof(cpu_set_t), &cpuset);
    if (s != 0)
    {
        handle_error_en(s, "pthread_setaffinity_np");
    }
    
    /* Check the actual affinity mask assigned to the thread */
    s = pthread_getaffinity_np(thread, sizeof(cpu_set_t), &cpuset);
    if (s != 0)
    {
        handle_error_en(s, "pthread_getaffinity_np");
    }
    
    printf("Set returned by pthread_getaffinity_np() contained:\n");
    for (j = 0; j < CPU_SETSIZE; j++) //CPU_SETSIZE 是定义在<sched.h>中的宏，通常是1024
    {
        if (CPU_ISSET(j, &cpuset))
        {
            printf("    CPU %d\n", j);
        }
    }
    exit(EXIT_SUCCESS);
}

例子四：使用seched_setaffinity设置线程的CPU亲和性

#define _GNU_SOURCE
#include <sched.h>
#include <stdlib.h>
#include <sys/syscall.h> // syscall

int main(void)
{
    pid_t tid;
    int i, nrcpus;
    cpu_set_t mask;
    unsigned long bitmask = 0;
    
    CPU_ZERO(&mask);
    CPU_SET(0, &mask); /* add CPU0 to cpu set */
    CPU_SET(2, &mask); /* add CPU2 to cpu set */

    // get tid(线程的PID，线程是轻量级进程，所以其本质是一个进程)
    tid = syscall(__NR_gettid); // or syscall(SYS_gettid);

      /* Set the CPU affinity for a pid */
    if (sched_setaffinity(tid, sizeof(cpu_set_t), &mask) == -1) 
    {
        perror("sched_setaffinity");
        exit(EXIT_FAILURE);
    }
    
    exit(EXIT_SUCCESS);
}