CPU_SWITCHTO(9)        NetBSD 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 cur-
     rently 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 func-
                tion 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 con-
                       text 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)

NetBSD 6.0                       June 2, 2011                       NetBSD 6.0

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