linux ns级定时器_转载_Linux下的hrtimer高精度定时器的使用

hrtimer高精度定时器的interval由ktime_set(const long secs, const unsigned long nsecs)决定，可做到ns级。此处的例子为5ms interval：

#include 

#include 

#include 

#include 

MODULE_LICENSE("GPL");

staticstructhrtimer hr_timer;

staticstructwork_struct wq_hrtimer;

staticktime_t ktime;

staticunsignedintinterval=5000;/* unit: us */

structtimespec uptimeLast;

staticunsignedintcount=0;

#define COUNT_INTERVAL 4000

unsigned longlongdiff_tv(structtimespec start,structtimespec end) {

return(end.tv_sec-start.tv_sec)*1000000000+(end.tv_nsec-start.tv_nsec);

}

enumhrtimer_restart my_hrtimer_callback(structhrtimer *timer )

{

schedule_work(&wq_hrtimer);

returnHRTIMER_NORESTART;

}

staticvoidwq_func_hrtimer(structwork_struct *work)

{

structtimespec uptime;

hr_timer.function = my_hrtimer_callback;

ktime = ktime_set( interval/1000000, (interval%1000000)*1000 );

hrtimer_start(&hr_timer, ktime, HRTIMER_MODE_REL );

/* print time every COUNT_INTERVAL*interval second*/

if(count%COUNT_INTERVAL==0)

{

do_posix_clock_monotonic_gettime(&uptime);

printk(KERN_INFO"hrtimer:%9lu sec, %9lu ns, interval_delay=%lu nsn",

(unsigned long) uptime.tv_sec, uptime.tv_nsec,

(unsigned long)(diff_tv(uptimeLast, uptime)-interval*1000*COUNT_INTERVAL) 

/COUNT_INTERVAL);

uptimeLast=uptime;

}

count++;

}

staticint__init module_hrtimer_init(void)

{

structtimespec uptime;

printk(KERN_INFO"HR Timer module installingn");

hrtimer_init( &hr_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL );

ktime = ktime_set( interval/1000000, (interval%1000000)*1000 );

hr_timer.function = my_hrtimer_callback;

hrtimer_start( &hr_timer, ktime, HRTIMER_MODE_REL );

do_posix_clock_monotonic_gettime(&uptime);

uptimeLast = uptime;

printk(KERN_INFO"hrtimer:%9lu sec, %9lu nsn", (unsignedlong) uptime.tv_sec,

uptime.tv_nsec );

INIT_WORK(&wq_hrtimer, wq_func_hrtimer);

return0;

}

staticvoid__exit module_hrtimer_exit(void)

{

intret;

ret = hrtimer_cancel( &hr_timer );

if(ret)

printk("The timer was still in use...n");

printk("HR Timer module uninstallingn");

return;

}

module_init(module_hrtimer_init);

module_exit(module_hrtimer_exit);

#include

#include

#include

#include

MODULE_LICENSE("GPL");

static struct hrtimer hr_timer;

static struct work_struct wq_hrtimer;

static ktime_t ktime;

static unsigned int interval=5000; /* unit: us */

struct timespec uptimeLast;

static unsigned int count=0;

#define COUNT_INTERVAL 4000

unsigned long long diff_tv(struct timespec start, struct timespec end) {

return (end.tv_sec-start.tv_sec)*1000000000+(end.tv_nsec-start.tv_nsec);

}

enum hrtimer_restart my_hrtimer_callback( struct hrtimer *timer )

{

schedule_work(&wq_hrtimer);

return HRTIMER_NORESTART;

}

static void wq_func_hrtimer(struct work_struct *work)

{

struct timespec uptime;

hr_timer.function = my_hrtimer_callback;

ktime = ktime_set( interval/1000000, (interval%1000000)*1000 );

hrtimer_start(&hr_timer, ktime, HRTIMER_MODE_REL );

/* print time every COUNT_INTERVAL*interval second*/

if(count%COUNT_INTERVAL==0)

{

do_posix_clock_monotonic_gettime(&uptime);

printk(KERN_INFO"hrtimer:%9lu sec, %9lu ns, interval_delay=%lu nsn",

(unsigned long) uptime.tv_sec, uptime.tv_nsec,

(unsigned long)(diff_tv(uptimeLast, uptime)-interval*1000*COUNT_INTERVAL)

/COUNT_INTERVAL);

uptimeLast=uptime;

}

count++;

}

static int __init module_hrtimer_init( void )

{

struct timespec uptime;

printk(KERN_INFO"HR Timer module installingn");

hrtimer_init( &hr_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL );

ktime = ktime_set( interval/1000000, (interval%1000000)*1000 );

hr_timer.function = my_hrtimer_callback;

hrtimer_start( &hr_timer, ktime, HRTIMER_MODE_REL );

do_posix_clock_monotonic_gettime(&uptime);

uptimeLast = uptime;

printk(KERN_INFO"hrtimer:%9lu sec, %9lu nsn", (unsigned long) uptime.tv_sec,

uptime.tv_nsec );

INIT_WORK(&wq_hrtimer, wq_func_hrtimer);

return 0;

}

static void __exit module_hrtimer_exit( void )

{

int ret;

ret = hrtimer_cancel( &hr_timer );

if (ret)

printk("The timer was still in use...n");

printk("HR Timer module uninstallingn");

return;

}

module_init(module_hrtimer_init);

module_exit(module_hrtimer_exit);

如果在my_hrtimer_callback()里面直接返回HRTIMER_RESTART会导致立即重新进入my_hrtimer_callback()。这时shell对输入没有任何响应。

所以为了解决这个问题，创建了一个work queue，由my_hrtimer_callback() enqueue这个工作队列。在work queue的处理函数里面重启hrtimer。

但是这样带来的负面影响是进入hrtimer_callback和wq_func被调用之间有Linux系统调度引入的延迟，导致interval出现误差。经过实测，在ZC706缺省配置下，这个延迟大约是17.5us (hrtimer interval为5ms，每20秒计算一次interval误差)。

root@zynq:~/nfs/hrtimer# insmod hrtimer.ko

HR Timer module installing

hrtimer:    2900 sec, 993366078 ns

hrtimer:    2900 sec, 998395278 ns, interval_delay=369966 ns

hrtimer:    2921 sec,  69525447 ns, interval_delay=17782 ns

hrtimer:    2941 sec, 139764655 ns, interval_delay=17559 ns

hrtimer:    2961 sec, 210029519 ns, interval_delay=17566 ns

hrtimer:    2981 sec, 280465631 ns, interval_delay=17609 ns

hrtimer:    3001 sec, 350677038 ns, interval_delay=17552 ns

hrtimer:    3021 sec, 420625114 ns, interval_delay=17487 ns

hrtimer:    3041 sec, 490744847 ns, interval_delay=17529 ns

root@zynq:~/nfs/hrtimer# insmod hrtimer.ko

HR Timer module installing

hrtimer: 2900 sec, 993366078 ns

hrtimer: 2900 sec, 998395278 ns, interval_delay=369966 ns

hrtimer: 2921 sec, 69525447 ns, interval_delay=17782 ns

hrtimer: 2941 sec, 139764655 ns, interval_delay=17559 ns

hrtimer: 2961 sec, 210029519 ns, interval_delay=17566 ns

hrtimer: 2981 sec, 280465631 ns, interval_delay=17609 ns

hrtimer: 3001 sec, 350677038 ns, interval_delay=17552 ns

hrtimer: 3021 sec, 420625114 ns, interval_delay=17487 ns

hrtimer: 3041 sec, 490744847 ns, interval_delay=17529 ns