int vfs_readdir(struct file *file, filldir_t filler, void *buf)
{
    struct inode *inode = file->f_ dentry->d_inode;
    int res = -ENOTDIR;
+   /* Introduce a millisecond bottleneck
+      (HZ is set to 1000 on this system) */
+   unsigned long timeout = jiffies+1;

+   while (time_before(jiffies, timeout));
+   /* End of bottleneck */

    /* ... */
    
}