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:
- cpu_switchto() does not switch address
spaces.
- 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).
- cpu_switchto() should be called at
IPL_SCHED. When the function returns, the caller
should lower the priority level as soon as possible.
- 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 exiting.
SEE ALSO
membar_producer(3),
swapcontext(3),
intro(9),
mutex(9),
spl(9)