static inline unsigned ccnt_read(void) {
        unsigned cc;
        __asm__ volatile ("mrc p15, 0, %0, c15, c12, 1" : "=r"(cc));
        return cc;
}

unsigned int lastx = 0;
void poke(unsigned long arg) {
        unsigned x = ccnt_read();
        printk(KERN_ALERT "tick %u %d\n",x,(x - lastx));
        lastx = x;
        timer.expires = jiffies + (HZ/FREQ);
        add_timer(&timer);
}

[  875.070623] tick 49848138 49848138
[  876.070637] tick 97284866 47436728
[  877.070660] tick 141050351 43765485
[  878.070671] tick 346197125 205146774
[  879.070687] tick 389887770 43690645
[  880.070702] tick 433868979 43981209
[  881.070717] tick 479485250 45616271
[  882.070734] tick 526325449 46840199
[  883.070750] tick 652657918 126332469
[  884.070768] tick 780097755 127439837