These functions are used to register and schedule software interrupt handlers.
Software interrupt handlers are attached to a software interrupt thread, just
as hardware interrupt handlers are attached to a hardware interrupt thread.
Multiple handlers can be attached to the same thread.
Software interrupt handlers can be used to queue up less critical processing
inside of hardware interrupt handlers so that the work can be done at a later
time.
Software interrupt threads are different from other kernel threads in that they
are treated as an interrupt thread.
This means that time spent executing these threads is counted as interrupt
time, and that they can be run via a lightweight context switch.
The
swi_add()
function is used to add a new software interrupt handler to a specified
interrupt event.
The
eventp
argument is an optional pointer to a
struct intr_event
pointer.
If this argument points to an existing event that holds a list of
interrupt handlers, then this handler will be attached to that event.
Otherwise a new event will be created, and if
eventp
is not
NULL,
then the pointer at that address to will be modified to point to the
newly created event.
The
name
argument is used to associate a name with a specific handler.
This name is appended to the name of the software interrupt thread that this
handler is attached to.
The
handler
argument is the function that will be executed when the handler is scheduled
to run.
The
arg
parameter will be passed in as the only parameter to
handler
when the function is executed.
The
pri
value specifies the priority of this interrupt handler relative to other
software interrupt handlers.
If an interrupt event is created, then this value is used as the vector,
and the
flags
argument is used to specify the attributes of a handler such as
INTR_MPSAFE.
The
cookiep
argument points to a
void *
cookie.
This cookie will be set to a value that uniquely identifies this handler,
and is used to schedule the handler for execution later on.
The
swi_remove()
function is used to teardown an interrupt handler pointed to by the
cookie
argument.
It detaches the interrupt handler from the associated interrupt event
and frees its memory.
The
swi_sched()
function is used to schedule an interrupt handler and its associated thread to
run.
The
cookie
argument specifies which software interrupt handler should be scheduled to run.
The
flags
argument specifies how and when the handler should be run and is a mask of one
or more of the following flags:
|
| SWI_DELAY
|
Specifies that the kernel should mark the specified handler as needing to run,
but the kernel should not schedule the software interrupt thread to run.
Instead,
handler
will be executed the next time that the software interrupt thread runs after
being scheduled by another event.
Attaching a handler to the clock software interrupt thread and using this flag
when scheduling a software interrupt handler can be used to implement the
functionality performed by
setdelayed()
in earlier versions of
FreeBSD .
|
| SWI_FROMNMI
|
| |
Specifies that
swi_sched()
is called from NMI context and should be careful about used KPIs.
On platforms allowing IPI sending from NMI context it immediately wakes
clk_intr_event
via the IPI, otherwise it works just like SWI_DELAY.
|
|
The
tty_intr_event
and
clk_intr_event
variables contain pointers to the software interrupt handlers for the tty and
clock software interrupts, respectively.
tty_intr_event
is used to hang tty software interrupt handlers off of the same thread.
clk_intr_event
is used to hang delayed handlers off of the clock software interrupt thread so
that the functionality of
setdelayed()
can be obtained in conjunction with
SWI_DELAY.
The
vm_ih
handler cookie is used to schedule software interrupt threads to run for the
VM subsystem.
