Cheat Engine

[Freiza]

Which takes more cpu time?
1) Switching between two processes.
2) Switching a process from user mode to kernel mode.
Considering the fact that switching between two process is done by cpu..

[Polynomial]

Your question is a little vague. Are we just talking about a context switch triggered by the thread manager? If so, switching between user and kernel space probably takes a couple extra cycles - but nothing noticeable even if we were to switch a few thousand times a second. The extra cycles account for switching the processor's active ring number (i.e. ring3 -> ring0 in this case) and performing whatever checks the OS likes to do.

If you're talking about manual invokation of code through direct call or an event, it depends on a lot of factors:

• How are you switching? A mutex is slower than two WaitForSingleObject wakeups on a global event.
  
• Are you performing direct calls? CreateRemoteThread should be a little faster than DeviceIoControl or a syscall.
  
• If I remember correctly, sometimes higher priority IO will cause a user->kernel dispatch to be delayed, or even allocated to be sent by DPC at a later time.
  

Give some more details and we can probably help more.