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IPI(9) Kernel Developer's Manual IPI(9)


ipiMI IPI interface


#include <sys/ipi.h>

typedef void (*ipi_func_t)(void *);

ipi_register(ipi_func_t func, void *arg);

ipi_unregister(u_int ipi_id);

ipi_trigger(u_int ipi_id, struct cpu_info *ci);

ipi_unicast(ipi_msg_t *msg, struct cpu_info *ci);

ipi_multicast(ipi_msg_t *msg, const kcpuset_t *target);

ipi_broadcast(ipi_msg_t *msg);

ipi_wait(ipi_msg_t *msg);


The machine-independent ipi interface provides capability to send inter-processor interrupts (IPIs) amongst CPUs. The interface has two mechanisms: asynchronous IPI to invoke functions with a constant argument and synchronous IPIs with the cross-call support.

Other synchronization interfaces are built using the MI IPI interface. For a general purpose inter-processor cross-calls or remote interrupts, use the xcall(9) or softint(9) interfaces.

The primary use cases of the MI IPIs include the following:

  • provide a facility for the softint(9) subsystem to schedule software interrupts on remote CPUs
  • provide a facility for the xcall(9) subsystem
  • abstract IPI handling and facilitate machine-dependent code

Asynchronous IPI interface

This interface allows dynamic registration of IPI handlers with a constant argument and asynchronous triggering of interrupts.
ipi_register(func, arg)
Register an IPI handler func with an arbitrary argument arg. Returns a non-zero IPI identifier on success and zero on failure.
Unregister the IPI handler identified by the ipi_id.
ipi_trigger(ipi_id, ci)
Trigger an IPI identified by ipi_id on a remote CPU specified by ci. This function must be called with the kernel preemption disabled and the target CPU must be remote.

Synchronous IPI interface

This interface provides capability to perform cross-calls, i.e. invoke an arbitrary function on a remote CPU. The invocations are performed synchronously and the caller must wait for completion. The cross-call is described by an IPI "message". The caller has to fill in an ipi_msg_t structure which has the following public members:

        ipi_func_t	func; 
        void		arg;

The func member specifies a function to invoke and arg is the argument to be passed to the function.

ipi_unicast(msg, ci)
Send an IPI to a remote CPU specified by ci.
ipi_multicast(msg, target)
Send IPIs to a CPU set specified by target.
Send IPIs to all CPUs.
Wait until all IPIs complete.

All described functions, except ipi_wait(), must be called with the kernel preemption disabled. All synchronous IPI invocations must be completed (wait for them with the ipi_wait() function) before the IPI message structure can be destroyed or new cross-call requests can be performed.


Functions being called must be lightweight. They run at IPL_HIGH and should generally not use any other synchronization interfaces such as mutex(9). If spin-locks are used, they must be used carefully and have no contention.


The ipi interface is implemented within the file sys/kern/subr_ipi.c.


The ipi interface first appeared in NetBSD 7.0.


Mindaugas Rasiukevicius <>
May 25, 2014 NetBSD 7.0