What is the code execution sequence of the driver and its test program?

What is the code execution sequence of the driver and its test program? -- Linux general technology-Linux programming and kernel information. The following is a detailed description. For example, the driver code has a function:
Static ssize_t xx_write (struct file * filp, const char _ user * buf, size_t size, loff_t * ppos)
{
.................
Printk (KERN_EMERG "kernel write \ n ");
.................
}
Its test code has a corresponding test function:
Printf ("call xx_write function \ n ");
Fwrite (Buf, sizeof (Buf), 1, fp0 );
Q: Do I print the content in printf or the content of printk first when running the test code ??

I personally think that the content of printf should be printed first, because this sentence is run first, but the experiment result is the opposite ?? Why? Please answer.