cpu_need_resched(9) [netbsd man page]

CPU_NEED_RESCHED(9)					   BSD Kernel Developer's Manual				       CPU_NEED_RESCHED(9)

NAME

     cpu_need_resched -- context switch notification

SYNOPSIS

     #include <sys/cpu.h>

     void
     cpu_need_resched(struct cpu_info *ci, int flags);

DESCRIPTION

     The cpu_need_resched() function is the machine-independent interface for the scheduler to notify machine-dependent code that a context switch
     from the current LWP, on the cpu ci, is required.	This event may occur if a higher priority LWP appears on the run queue or if the current
     LWP has exceeded its time slice.

     If RESCHED_KPREEMPT flag is specified in flags and __HAVE_PREEMPTION C pre-processor macro is defined in <machine/intr.h>, machine-dependent
     code should make a context switch happen as soon as possible even if the cpu is running the kernel code.

     If RESCHED_IMMED flag is specified in flags, machine-dependent code should make a context switch happen as soon as possible.  In that case,
     for example, if ci is not the current processor, cpu_need_resched() typically issues an inter processor call to the processor to make it
     notice the need of a context switch as soon as possible.

     Typically, the cpu_need_resched() function will perform the following operations:

	   o   Set a per-processor flag which is checked by userret(9) when returning to user-mode execution.

	   o   Post an asynchronous software trap (AST).

	   o   Send an inter processor interrupt to wake up cpu_idle(9).

SEE ALSO

     sched_4bsd(9), userret(9)

BSD
								   July 31, 2010							       BSD

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

NAME

     cpu_switchto -- machine-dependent LWP context switching interface

SYNOPSIS

     #include <sys/cpu.h>

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

DESCRIPTION

     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.

     Remarks:

	   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
		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.

RETURN VALUES

     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-
     ing.

SEE ALSO

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

BSD
								   June 2, 2011 							       BSD