Cortex-M3: clock cycles counter

Hi folks,

I'm trying to do some sort of profiling for the Cortex-M3 on the MCBSTM32C board.
In particular, I have to establish how many clock cycles are needed for the execution of a specific algorithm. To this aim, I'm using the following code:

// variable definitions
uint32_t clock_cycles_counter;
volatile unsigned int *DWT_CYCCNT = (uint32_t *)0xE0001004; //address of the register
volatile unsigned int *DWT_CONTROL = (uint32_t *)0xE0001000; //address of the register
volatile unsigned int *SCB_DEMCR = (uint32_t *)0xE000EDFC; //address of the register

[...]

// configure and start the clock cycles counter
clock_cycles_counter = 0;
*SCB_DEMCR = *SCB_DEMCR | 0x01000000;
*DWT_CYCCNT = 0;
*DWT_CONTROL |=  1;

// do something
algorithm();

// stop and get the counter value
*DWT_CONTROL &= ~1;
clock_cycles_counter = *DWT_CYCCNT;

// print the counter value
printf("%d\n\r", clock_cycles_counter);

This code works, but something strange is happening. In particular, if I change the last printf() with this one:

printf("%s %d\n\r", "test", clock_cycles_counter);

The printed clock cycles value is different. I guess it shouldn't be the case, because the clock cycles counter has been already set when the printf() executes.

I've also tried to do some debug, like multiple printf() (one after an other) and each one prints the same value.

Unfortunately, I can't see the disassembly since I'm trying the free versione of the Keil toolchain.

Any hint would be greatly appreciated!

Thank you,
Pierpaolo