MI_SWITCH(9) | Kernel Developer's Manual | MI_SWITCH(9) |
mi_switch
—
mi_switch
(struct
lwp *l);
mi_switch
() function implements the
machine-independent prelude to an LWP context switch. It is called from only a
few distinguished places in the kernel code as a result of the principle of
non-preemptable kernel mode execution. The three major uses of
mi_switch
() can be enumerated as follows:
mi_switch
() records the amount of time the
current LWP has been running in the LWP structure and checks this value
against the CPU time limits allocated to the LWP (see
getrlimit(2)). Exceeding
the soft limit results in a SIGXCPU
signal to be
posted to the LWP, while exceeding the hard limit will cause a
SIGKILL
.
Unless l->l_switchto is not
NULL
, mi_switch
() will call
sched_nextlwp
() to select a new LWP from the
scheduler's runqueue structures. If no runnable LWP is found, the idle LWP
is used. If the new LWP is not equal to the current one,
mi_switch
() will hand over control to the
machine-dependent function
cpu_switchto(9) to
switch to the new LWP.
mi_switch
() has to be called with the LWP
lock held (through calling lwp_lock
() first) and at
the splsched(9) interrupt
protection level. It returns with the LWP lock released.
mi_switch
() returns 1 if a context switch was performed
to a different LWP, 0 otherwise.
July 21, 2007 | NetBSD 9.2 |