I was looking at the sources of ethtool, particularly at function do_spause() where autonegotiation, rx/tx pause can be enabled/disabled. I noticed that at first it issues ioctl() for ETHTOOL_GPAUSEPARAM command, i.e. it fetches the current settings, and they're the same, it doesn't change anything, otherwise it will issue ioctl() with ETHTOOL_SPAUSEPARAM command and set new parameters.
What is the reason for this? Is this optimization, or way to avoid link disruption?