Inter-processor interrupt: Difference between revisions

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{{short description|Type of interrupt signal sent between computer processors}}

{{mergefrom:Shoulder tap (software)}}

{{UnreferencedMore references|date=December 20092014}}

An '''inter-processor interrupt''' ('''IPI''') is a special type of [[interrupt]] by which one processor may interrupt another processor in a [[multiprocessor]] system. IPIs are typically used to implement a [[cache coherency]] [[synchronization]] point.

AnIn [[computing]], an '''inter-processor interrupt''' ('''IPI'''), also known as a ''shoulder tap'', is a special type of [[interrupt]] by which one [[Processor (computing)|processor]] may interrupt another processor in a [[multiprocessor]] system. IPIsif arethe typicallyinterrupting usedprocessor torequires implementaction afrom [[cachethe coherency]]other [[synchronization]] pointprocessor. Actions that might be requested include:

== Mechanism ==

IPI signalling is often performed through the use of the [[Advanced Programmable Interrupt Controller|APIC]]. When a CPU wishes to send an interrupt to another CPU, it stores the interrupt vector and the identifier of the target's local APIC in the Interrupt Command Register (ICR) of its own local APIC. A message is then sent via the APIC bus to the target's local APIC, which therefore issues a corresponding interrupt to its own CPU.

* Flush [[memory management unit]] caches, such as [[translation lookaside buffer]]s, on other processors when memory mappings are changed by one processor;

== Examples ==

* Stop when the system is being shut down by one processor.

* Notify an alternate CPU of a malfunction for Alternate CPU Recovery (ACR).

* Notify a processor that higher-priority work is available.

* Notify a processor of work that cannot be done on all processors due to, e.g.,

** asymmetric access to [[I/O channel]]s<ref>{{cite manual

| title = OS I/O Supervisor Logic - Release 21 - Program Number 360S-CI-505

| id = GY28-6616-9

| page = 271

| section = Appendix F: Multiprocessing Extensions

| section-url = http://bitsavers.org/pdf/ibm/360/os/R21.7_Apr73/plm/GY28-6616-9_OS_IO_Superv_PLM_R21.7_Apr73.pdf#page=282

| url = http://bitsavers.org/pdf/ibm/360/os/R21.7_Apr73/plm/GY28-6616-9_OS_IO_Superv_PLM_R21.7_Apr73.pdf

| series = Program Logic

| publisher = [[IBM]]

| access-date = August 28, 2022

}}

</ref>

** special features on some processors<ref>{{Cite web |title=AMD Technical Information Portal |url=https://docs.amd.com/r/en-US/am011-versal-acap-trm/Inter-Processor-Interrupts |access-date=2024-07-18 |website=docs.amd.com}}</ref>

=== WindowsMechanism ===

The [[OS/360 and successors#M65MP|M65MP]] option of [[OS/360 and successors|OS/360]] used the Direct Control feature of the [[IBM System/360|S/360]] to generate an interrupt on another processor; on [[IBM System/370|S/370]] and its successors, including [[z/Architecture]], the SIGNAL PROCESSOR instruction provides a more formalized interface. The documentation for some IBM operating systems refers to this as a shoulder tap.

In a [[Microsoft Windows]] based multiprocessor system, a processor may interrupt another processor for the following reasons:

IPIOn signalling[[IBM isPC oftencompatible]] performedcomputers through thethat use of the [[Advanced Programmable Interrupt Controller|APIC]] (APIC), IPI signaling is often performed using the APIC. When a CPU wishes to send an interrupt to another CPU, it stores the [[interrupt vector]] and the identifier of the target's local APIC in the Interrupt Command Register (ICR) of its own local APIC. A message is then sent via the APIC bus to the target's local APIC, which thereforethen issues a corresponding interrupt to its own CPU.

1. Queue a DISPATCH_LEVEL interrupt to schedule a particular thread for execution.<br />

2. Updating the processor's [[translation lookaside buffer]]s cache.<br />

3. System shutdown.<br />

4. System crash.<br />

5. Kernel debugger breakpoint.

== Examples ==

IPIs are given an [[IRQL (Windows)|IRQL]] of 29.

In a multiprocessor system running [[Microsoft Windows]], a processor may interrupt another processor for the following reasons, in addition to the ones listed above:<ref>{{Cite web |title=Inter Processor Interrupt usage |url=https://stackoverflow.com/questions/15091165/inter-processor-interrupt-usage |access-date=2024-07-18 |website=Stack Overflow |language=en}}</ref>

1.# Queuequeue a DISPATCH_LEVEL interrupt to schedule a particular thread for execution.<br />;

=== Linux/Unix ===

5.# Kernelkernel debugger breakpoint.

In Unix/Linux, the IPI interrupt is often used by the CPU in the [[Symmetric multiprocessor|SMP]] and [[Asymmetric multiprocessing|AMP]] configurations to communicate with other processors in the setup.

IPIs are given an [[IRQL (Windows)|IRQL]] of 29.<ref>{{cite web

== Other uses ==

|author = Matt

In [[x86 architecture|x86]] based systems, an IPI synchronizes the cache and [[memory management unit]] (MMU) between processors.

|title = Understanding IRQL

|url = https://ext2fsd.sourceforge.net/documents/irql.htm

|accessdate = 2014-12-06

|date = 2002-04-28

|archive-date = 2019-10-14

|archive-url = https://web.archive.org/web/20191014125625/http://ext2fsd.sourceforge.net/documents/irql.htm

|url-status = dead

}}</ref>

==See also==

* [[Advanced Programmable Interrupt Controller]] (APIC)

* [[Interrupt]]

* [[Interrupt handler]]

* [[Non-maskable interrupt]] (NMI)

* [[Programmable Interrupt Controller]] (PIC)

== References ==

{{Reflist}}

== External links ==

*[http://linux.linti.unlp.edu.ar/images/0/0c/ULK3-CAPITULO4-UNNOBA.pdf Interrupts and Exceptions]

{{DEFAULTSORT:Inter-Processor Interrupt}}

[[Category:Interrupts]]