CPU consumption of process spawned by a service

Hi,

A win32 application during its run time creates a process using CreateProcess() API.

I find the process comsumes more CPU when it's parent Win32 application is running as a service compared to when it's parent Win32 application is running as standard application.

For example, consider a Win32 application temp.exe.
** temp.exe is run as standard application. During runtime it creates a process proc.exe. proc.exe consumes 60% CPU.
** temp.exe is run as service. During runtime it creates a process proc.exe. proc.exe consumes 80% CPU.

Can anyone help me understand why this difference in CPU consumption is seen.

Thanks,
Anandhi