【Linux设备驱动程序（第三版）】----延迟：让出处理器

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#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/init.h>
#include <linux/time.h>
#include <linux/timer.h>
#include <linux/proc_fs.h>
#include <linux/spinlock.h>
#include <linux/interrupt.h>
#include <asm/hardirq.h>
#include <linux/sched.h>//jiffies
#include <linux/kernel.h>
#include <linux/types.h>//u64
#include <linux/fs.h>//file_operations, file
#include <linux/completion.h>
#include <asm/uaccess.h>//copy_to_user & copy_from_user

int delay = HZ;

enum jit_files {
	JIT_BUSY,
	JIT_SCHED,
	JIT_QUEUE,
	JIT_SCHEDTO
};

int jit_fn(char *buf, char **start, off_t offset, int len, int *eof, void *data)
{
	unsigned long j0, j1;
	wait_queue_head_t wait;

	init_waitqueue_head(&wait);
	j0 = jiffies;
	j1 = j0 + delay;

	switch((long)data){
		case JIT_BUSY:
			while(time_before(jiffies, j1))
				cpu_relax();
			break;
		case JIT_SCHED:
			while(time_before(jiffies, j1))
				schedule();
			break;
	}
	j1 = jiffies;
	len = sprintf(buf, "%9li %9lin", j0, j1);
	*start = buf;
	return len;
}

int jit_currentime(char *buf, char **start, off_t offset, int len, int *eof, void *data)
{
	struct timeval tv1;
	struct timespec tv2;
	unsigned long j1;
	u64 j2;

	j1 = jiffies;
	j2 = get_jiffies_64();
	do_gettimeofday(&tv1);
	tv2 = current_kernel_time();
	
	len = 0;
	len += sprintf(buf,"0x%08lx 0x%016Lx %10i.%06in"
		       "%40i.%09in",
		       j1, j2,
		       (int) tv1.tv_sec, (int) tv1.tv_usec,
		       (int) tv2.tv_sec, (int) tv2.tv_nsec);
	*start = buf;
	return len;
}

int __init jit_init(void)
{
	create_proc_read_entry("jit_currentime", 0, NULL, jit_currentime, NULL);
	create_proc_read_entry("jitbusy", 0, NULL, jit_fn, (void *)JIT_BUSY);
	create_proc_read_entry("jitsched", 0, NULL, jit_fn, (void *)JIT_SCHED);
	return 0;
}

void __exit jit_exit(void)
{
	remove_proc_entry("jit_currentime", NULL);
	remove_proc_entry("jitbusy", NULL);
	remove_proc_entry("jitsched", NULL);
}

MODULE_LICENSE("Dual BSD/GPL");
module_init(jit_init);
module_exit(jit_exit);

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obj-m:= jit.o
modules-objs:= jit.o

KDIR:= /usr/src/linux-headers-2.6.31-14-generic/
PWD:= $(shell pwd)

default:
	make -C $(KDIR) M=$(PWD) modules
clean:
	rm -rf *.ko *.mod.c *.mod.o *.o *.markers *.symvers *.order

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insmod jit.ko

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dd bs=20 count=5 < /proc/jitsched

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rmmod jit