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KTHREAD(9) NetBSD Kernel Developer's Manual KTHREAD(9)
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kthread_create, kthread_exit, kthread_join, kthread_fpu_enter,
kthread_fpu_exit -- kernel threads
kthread_create(pri_t pri, int flags, struct cpu_info *ci,
void (*func)(void *), void *arg, lwp_t **newlp, const char *fmt,
Kernel threads are light-weight processes which execute entirely within
Any process can request the creation of a new kernel thread. Kernel
threads are not swapped out during memory congestion. The VM space and
limits are shared with proc0 (usually swapper).
If the machine has any per-CPU floating-point units or SIMD vector units
that are normally available to user threads, they can be used by kthreads
between kthread_fpu_enter() and kthread_fpu_exit().
kthread_create(pri, flags, ci, func, arg, newlp, fmt, ...)
Create a kernel thread. The arguments are as follows.
pri Priority level for the thread. If no priority level is
desired specify PRI_NONE, causing kthread_create() to
select the default priority level.
flags Flags that can be logically ORed together to alter the
ci If non-NULL, the thread will be created bound to the
CPU specified by ci, meaning that it will only ever
execute on that CPU. By default, the threads are free
to execute on any CPU in the system.
func A function to be called when the thread begins execut-
ing. This function must not return. If the thread
runs to completion, it must call kthread_exit() to
properly terminate itself.
arg An argument to be passed to func(). May be NULL if not
newlp A pointer to receive the new LWP structure for the ker-
nel thread. May be NULL, unless KTHREAD_MUSTJOIN is
specified in flags.
fmt A string containing format information used to display
the kernel thread name. Must not be NULL.
The following flags are defined.
KTHREAD_IDLE Causes the thread to be created in the LSIDL
(idle) state. By default, the threads are
created in the LSRUN (runnable) state, meaning
they will begin execution shortly after cre-
KTHREAD_MPSAFE Specifies that the thread does its own locking
and so is multiprocessor safe. If not speci-
fied, the global kernel lock will be held
whenever the thread is running (unless explic-
itly dropped by the thread).
KTHREAD_INTR Specifies that the thread services device
interrupts. This flag is intended for kernel
internal use and should not normally be speci-
KTHREAD_TS Causes the kthread to be created in the
SCHED_OTHER class (timeshared). The thread's
priority will be dynamically adjusted by the
scheduler. Increased activity by the kthread
will cause its priority to fall; decreased
activity will cause its priority to rise. By
default, kthreads are created in the SCHED_RR
class, with a fixed priority specified by pri.
Threads in the SCHED_RR class do not have
their priority dynamically adjusted by the
KTHREAD_MUSTJOIN Indicates that created kthread must be joined.
In such case kthread_exit() will wait until
kthread_join() will be called.
Exit from a kernel thread. Must only be called by a kernel
Suspend execution of calling thread until the target kthread
terminates. Conceptually the function can be compared to the
user space pthread_join(3), however it must be called only once
for kernel thread which was created using the KTHREAD_MUSTJOIN
flag and would wait on kthread_exit.
Allow the current kthread to use any machine-dependent per-CPU
floating-point units or SIMD vector units normally available to
user threads. Returns a cookie that must be passed to
kthread_fpu_exit() when done.
Matching pairs of kthread_fpu_enter() and kthread_fpu_exit() may
Restore the current kthread's access to machine-dependent per-
CPU floating-point units or SIMD vector units to what it was
before the call to kthread_fpu_enter() that returned s.
On the last kthread_fpu_exit(), zero all the units' registers to
avoid leaking secrets -- such units are often used for cryptog-
Upon successful completion, kthread_create() returns 0. Otherwise, the
following error values are returned:
[EAGAIN] The limit on the total number of system processes would be
exceeded; or the limit RLIMIT_NPROC on the total number of pro-
cesses under execution by this user id would be exceeded.
The kthread framework itself is implemented within the file
sys/kern/kern_kthread.c. Data structures and function prototypes for the
framework are located in sys/sys/kthread.h.
condvar(9), driver(9), softint(9), workqueue(9)
The kthread framework appeared in NetBSD 1.4.
NetBSD 9.99 April 21, 2015 NetBSD 9.99
Modified for NetBSD
by Kimmo Suominen