内核必须懂(五): per-CPU变量

#include <iostream>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <string>

using namespace std;

#define NUM_THREADS 20 

// 文件描述符
int fd = 0;

// 多线程调用函数
void *pthread_fx( void *args ) {
    ioctl( fd, 1, 0 );
}

int main() {
    int ret = 0;
    
    // 打开文件
    if((fd = open("/dev/hellodr", O_RDWR)) < 0) {
        cerr << strerror(errno) << endl;
        return -1;
    }

    // 开启多线程
    pthread_t tids[NUM_THREADS];
    for ( int i = 0; i < NUM_THREADS; ++i ) {
        ret = pthread_create( &tids[i], NULL, pthread_fx, NULL );
        if ( ret != 0 ) {
            printf( "pthread_create error: error_code = %d\n", ret );
        }
    }

    // 回收线程资源
    for ( int i = 0; i < NUM_THREADS; ++i ) {
        pthread_join(tids[i], NULL);
    }

    // 关闭文件
    close( fd );
    
    return 0;
}

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>

#define    MAJOR_NUM    231
#define    DEVICE_NAME  "hellodr"

DEFINE_PER_CPU( long, gUsage ) = 0;

int DriverOpen( struct inode *pslINode, struct file *pslFileStruct )
{
    printk( KERN_ALERT DEVICE_NAME " hello open.\n" );
    return(0);
}


ssize_t DriverWrite( struct file *pslFileStruct, const char __user *pBuffer, size_t nCount, loff_t *pOffset )
{
    printk( KERN_ALERT DEVICE_NAME " hello write.\n" );
    return(0);
}


int DriverClose( struct inode *pslINode, struct file *pslFileStruct )
{
    int     i       = 0;
    unsigned long   ulBaseAddr  = 0;
    unsigned long   ulOffset    = 0;
    long        *pUsage     = NULL;
    long        usageSum    = 0;

    ulOffset = (unsigned long) (&gUsage);
    for_each_online_cpu( i )
    {
        ulBaseAddr  = __per_cpu_offset[i];
        pUsage      = (long *) (ulBaseAddr + ulOffset);
        usageSum    += (*pUsage);
        printk( KERN_ALERT DEVICE_NAME " pUsage = %lx, *pUsage = %ld\n", (unsigned long) pUsage, *pUsage );
    }
    printk( KERN_ALERT DEVICE_NAME " %ld\n", usageSum );

    return(0);
}


long DriverIOControl( struct file *pslFileStruct, unsigned int uiCmd, unsigned long ulArg )
{
    long *pUsage = NULL;
    /* printk( KERN_ALERT DEVICE_NAME ": pUsage = 0x%lx %lx %ld", (unsigned long) pUsage, (unsigned long) (&gUsage), (*pUsage) ); */
    preempt_disable();
    pUsage = this_cpu_ptr( (long *) (&gUsage) );
    (*pUsage)++;
    preempt_enable();
    return(0);
}


struct file_operations hello_flops = {
    .owner      = THIS_MODULE,
    .open       = DriverOpen,
    .write      = DriverWrite,
    .release    = DriverClose,
    .unlocked_ioctl = DriverIOControl
};

static int __init hello_init( void )
{
    int ret;

    ret = register_chrdev( MAJOR_NUM, DEVICE_NAME, &hello_flops );
    if ( ret < 0 )
    {
        printk( KERN_ALERT DEVICE_NAME " can't register major number.\n" );
        return(ret);
    }
    printk( KERN_ALERT DEVICE_NAME " initialized.\n" );
    return(0);
}


static void __exit hello_exit( void )
{
    printk( KERN_ALERT DEVICE_NAME " removed.\n" );
    unregister_chrdev( MAJOR_NUM, DEVICE_NAME );
}


module_init( hello_init );
module_exit( hello_exit );
MODULE_LICENSE( "GPL" );
MODULE_AUTHOR( "Sean Depp" );

preempt_disable();
pUsage = this_cpu_ptr( (long *) (&gUsage) );
(*pUsage)++;
preempt_enable();