Advanced Programmable Interrupt Controller: Difference between revisions

Revision as of 21:16, 19 February 2020

Revision as of 23:10, 19 April 2020

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The APIC timer had its initial acceptance woes. A Microsoft document from 2002 (which advocated for the adoption of [[High Precision Event Timer]] instead) criticized the LAPIC timer for having "poor resolution" and stating that "the clocks silicon is sometimes very buggy".<Ref>[http://msdn.microsoft.com/en-us/library/windows/hardware/gg463347.aspx Guidelines For Providing Multimedia Timer Support], September 20, 2002</ref> Nevertheless, the APIC timer is used for example by [[Windows 7]] when [[Profiling (computer programming)|profiling]] is enabled, and by [[Windows 8]] in all circumstances. (Before Windows 8 claimed exclusive rights to this timer, it was also used by some programs like [[CPU-Z]].) Under Microsoft Windows the APIC timer is not a shareable resource.<ref>[http://social.msdn.microsoft.com/Forums/windowsdesktop/en-US/5d075378-a45f-433b-a3f7-73f974ec962f/windows-8-and-apic-timer?forum=wdk Windows 8 and APIC timer] {{webarchive |url=https://web.archive.org/web/20140222070735/http://social.msdn.microsoft.com/Forums/windowsdesktop/en-US/5d075378-a45f-433b-a3f7-73f974ec962f/windows-8-and-apic-timer?forum=wdk |date=February 22, 2014 }}</ref>

The aperiodic interrupts offered by the APIC timer are used by the [[Linux kernel]] from[[tickless kernel]]
feature. This optional but default feature is new with 2.6.18. onwards toWith implementit itsenabled [[ticklesson kernel]]a feature;computer with an APIC timer, the legacykernel does not use the [[8253]] [[Programmable Interval Timer]] is no longer used by ticklessfor kernelstimekeeping.<ref>{{cite web|url=http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1005802|title=VMware Knowledge Base|website=kb.vmware.com}}</ref> A [[VMware]] document notes that "software does not have a reliable way to determine its frequency. Generally, the only way to determine the local APIC timer’s frequency is to measure it using the PIT or CMOS timer, which yields only an approximate result."<ref name="vmware">[http://www.vmware.com/files/pdf/Timekeeping-In-VirtualMachines.pdf Timekeeping in VMware Virtual Machines (for VMware vSphere 5.0, Workstation 8.0, Fusion 4.0)], page 8</ref>

==I/O APICs==