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NetBSD 6.1.5 - man page for cpu_switchto (netbsd section 9)

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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-inter-
		locked 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 call-
		       ing 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 block-
		       ing.  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
     exiting.

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

BSD					   June 2, 2011 				      BSD
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