Many a times i read/hear the argument that making a lot of system calls etc would be inefficient since the application make a mode switch i.e goes from user mode to kernel mode and after executing the system call starts executing in the user mode by making a mode switch again.
My question is what is the overhead of a mode switch ? Does cpu cache gets invalidated or tlb entries are flushed out or what happens that causes overhead ?
Please note that i am asking about the overhead involved in mode switch and not context switch. I know that mode switch and context switch are two different things and i am fully aware about overhead associated with a context switch, but what i fail to understand is what overhead is caused by a mode switch ?
If its possible please provide some information about a particular *nix platform like Linux, FreeBSD, Solaris etc.
Regards
lali