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
Linux下查看CPU相关信息, CPU的信息主要都在/proc/cupinfo中
shell
# 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:|uniqLinux查看某个进程运行在哪个逻辑CPU上
shell
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 3Linux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。
shell
//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
shell
# 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.
c
#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
c
#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):
shell
[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
c
#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.
c
#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
c
#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);
}