If you need to toggle a pin on STM32 micro controller as fast as possible the code bellow will help you achieve that.

void main()
{
 unsigned long *ptr;
 unsigned long val = 2;
 unsigned long val1 = 2ul << 16;
 GPIO_Config(&GPIOB_BASE, _GPIO_PINMASK_1,  _GPIO_CFG_DIGITAL_OUTPUT |
 _GPIO_CFG_SPEED_MAX | _GPIO_CFG_OTYPE_PP | _GPIO_CFG_PULL_NO);
 ptr = (unsigned long *)&GPIOB_BSRR;
 while(1)
 {
  *ptr = val;
  *ptr = val1;
  *ptr = val;
  *ptr = val1;
 }
}