CPU_SWITCHTO(9) BSD Kernel Developer's Manual CPU_SWITCHTO(9)
cpu_switchto -- machine-dependent LWP context switching interface
cpu_switchto(lwp_t *oldlwp, lwp_t *newlwp, bool returning);
The cpu_switchto() function saves the context of the LWP which is currently running on the processor, and restores the context of the LWP
specified by newlwp.
1. cpu_switchto() does not switch address spaces.
2. cpu_switchto() sets curlwp(9) to newlwp. If the architecture does non-interlocked adaptive mutex release, cpu_switchto() does an
equivalent of membar_producer(3), before and after the modification of curlwp(9).
3. cpu_switchto() should be called at IPL_SCHED. When the function returns, the caller should lower the priority level as soon as
4. cpu_switchto() might be called with spin mutexes held.
The function takes the following arguments.
oldlwp Specify the LWP from which the switch is going to be made, i.e., the calling LWP. If it was NULL, the context of the LWP
currently running on this processor is not saved.
newlwp Specify the LWP to which to switch. It must not be NULL.
returning Only meaningful if the architecture implements fast software interrupts. If true, it indicates that oldlwp is a soft
interrupt LWP that is blocking. It is a good indication that any kind of address space or user activity can be completely
ignored. For example: ras_lookup(9), cache flushes, TLB wirings, adjusting lazy FPU state. All that is required is to
restore the register state and stack, and return to the interrupted LWP.
The cpu_switchto() function does not return until another LWP calls cpu_switchto(). It returns the oldlwp argument of the cpu_switchto()
which is called to switch back to our LWP. It is either a LWP which called cpu_switchto() to switch to us or NULL in case the LWP was exit-
membar_producer(3), swapcontext(3), intro(9), mutex(9), spl(9)
June 2, 2011 BSD