>"context switch to and from the kernel" This is a common misconception, a "context" switch is a lot more expensive than a "mode" switch that goes from user mo

>"context switch to and from the kernel" This is a common misconception, a "context" switch is a lot more expensive than a "mode" switch that goes from user mode to the kernel mode (and back). Of course, if the futex has to wait, it'd be a context switch for real.