I have tried to set core affinity of smss.exe to not run on one critical core on Windows 7 and Windows Server 2008r2. It turns out that simply setting the core affinity to anything (even the full mask that smss.exe already has) seems to work but prevents users from rdp'ing into the machine until it is restarted. The users already logged in may continue to use their sessions. This behaviour does not occur on Windows 8/Windows Server 2012. Does anyone know why it is happening?