Multithreaded programming thread binding processor Kernel __ programming

Source: http://blog.renren.com/share/30860442/5821521068

Linux systems provide API functions sched_setaffinity and sched_getaffinity used to set or obtain the available CPU cores for a thread.

int sched_setaffinity (pid_t pid, unsigned int cpusetsize, cpu_set_t *mask);

The PID in this function represents the thread ID (or process ID) that needs to set or get the binding information, if 0, the current calling thread is set, and the 2nd parameter cpusetsize is generally set to sizeof (cpu_set_t). The size of the memory structure object that the 3rd argument points to, and the 3rd parameter mask a pointer to the type CPU_SET_T object that sets or gets the list of CPU cores that the specified thread can use. Linux provides functions Cpu_zero, Cpu_set, and Cpu_isset operate on objects of cpu_set_t type, where Cpu_zero is used to empty the contents of the Cpu_set_t type object, Cpu_set is used to set the Cpu_set_t type Object , Cpu_isset is used to determine whether the corresponding bit of the cpu_set_t type object and the kernel is set. The following is a simple code example to illustrate the specific uses of these two functions.

To set the thread binding code:

cpu_set_t Mask;

int blist[8]={2, 5, 13, 9, 3, 6, 7, 4}; Set the list of cores that need to be bound

#pragma omp parallel Private (mask)

{

Cpu_zero (&mask);

Cpu_set (Blist[omp_get_thread_num ()], &mask); To set the binding scheme for each thread

Sched_setaffinity (0,sizeof (cpu_set_t), &mask);

}

This code binds the 8 threads in the Paralle region to the kernel 2,5,13,9,3,6,7,4 in turn. You can also use the sched_getaffinity function to get a list of the available cores for a thread, as shown in the sample code:

int num_processors = sysconf (_sc_nprocessors_conf); Gets the number of current node cores

cpu_set_t get;

int i = 0;

Cpu_zero (&get);

Sched_getaffinity (0, sizeof (cpu_set_t), &get); Gets the available kernel for the current calling thread

for (i = 0; i < num_processors; i++)

{

if (Cpu_isset (i, &get))

{

printf ("The current thread%d bound to core%d\n", Omp_get_thread_num (), i);

}

}

The following is a complete example

File bind.c

#include <stdlib.h>

#include <stdio.h>

#include <sys/types.h>

#include <sys/sysinfo.h>

#include <unistd.h>

#define __use_gnu

#include <sched.h>

#include <ctype.h>

#include <string.h>

#include <pthread.h>

Maximum number of processes in the #define THREAD_MAX_NUM 100//1 CPUs

int num=0; Number of cores in CPU

void* Threadfun (void* arg)//arg pass thread label (own definition)

{

cpu_set_t Mask; The collection of CPU cores

cpu_set_t get; Gets the CPU in the collection

int *a = (int *) arg;

printf ("The A is:%d\n", *a); Display is the first few threads

Cpu_zero (&mask); Empty

Cpu_set (*a,&mask); Set Affinity values

if (sched_setaffinity (0, sizeof (mask), &mask) = = 1)//Set Thread CPU affinity

{

printf ("Warning:could not set CPU affinity, continuing...\n");

}

while (1)

{

Cpu_zero (&get);

if (sched_getaffinity (0, sizeof (GET), &get) = = 1)//Acquire thread CPU affinity

{

printf ("Warning:cound not get thread affinity, continuing...\n");

}

int i;

for (i = 0; i < num; i++)

{

if (Cpu_isset (i, &get))//Determine which CPU the thread is affinity with

{

printf ("This thread%d is running processor:%d\n", i,i);

}

}

}

return NULL;

}

int main (int argc, char* argv[])

{

num = sysconf (_sc_nprocessors_conf); Get the number of cores

pthread_t Thread[thread_max_num];

printf ("System has%i processor (s)." \ n ", num);

int Tid[thread_max_num];

int i;

for (i=0;i<num;i++)

{

Tid[i] = i; Each thread must have a tid[i]

Pthread_create (&thread[0],null,threadfun, (void*) &tid[i]);

}

for (i=0; i< num; i++)

{

Pthread_join (thread[i],null);/Waiting for all threads to end, thread to dead loop so Ctrl + C ends

}

return 0;

}

Compile command: gcc bind.c-o bind-lpthread

Execution:./bind

Output result: slightly

Special attention:

#define __USE_GNU Don't write #define _USE_GNU.

#include <pthread.h> must be written after #define __USE_GNU, otherwise the compilation will report an error

View your thread situation you can use top-h in another window at execution time to view the threads, view the individual cores, use the top command, and then press the number "1" to view it.