CPU_SWITCHTO(9) Kernel Developer's Manual CPU_SWITCHTO(9)

cpu_switchto — machine-dependent LWP context switching interface

#include <sys/cpu.h>

lwp_t *
cpu_switchto(lwp_t *oldlwp, lwp_t *newlwp, bool returning);

The () function saves the context of the LWP which is currently running on the processor, and restores the context of the LWP specified by newlwp.

Remarks:

  1. () 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 possible.
  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 exiting.

membar_producer(3), swapcontext(3), intro(9), mutex(9), spl(9)

June 2, 2011 NetBSD 11.0