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From: John Baldwin <jhb@FreeBSD.org>
To: "Wilkinson, Alex" <alex.wilkinson@dsto.defence.gov.au>
Date: Wed, 22 Jun 2005 11:02:36 -0400
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Cc: Emanuel Strobl <Emanuel.strobl@gmx.net>,
	Dag-Erling =?iso-8859-1?q?Sm=F8rgrav?= <des@des.no>,
	freebsd-current@freebsd.org
Subject: Re: lapic@2k interrukts eating CPU cycles
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On Wednesday 22 June 2005 09:07 am, Wilkinson, Alex wrote:
>     0n Wed, Jun 22, 2005 at 09:06:18AM +0200, Dag-Erling Smrgrav wrote:
>     >Emanuel Strobl <Emanuel.strobl@gmx.net> writes:
>     >> I don't know what lapic stands for (the l, if apic means
>     >> AdvancedProgrammableInterruptController)
>     >
>     >local, meaning per-CPU as opposed to the IOAPIC which is located in
>     >the south bridge and shared by all CPUs.
>
> Why do we need both LAPIC *and* an IO-APIC ?

Interrupt lines from devices are wired up to I/O APICs which is similar to the 
8259A AT PICs.  Local APICs are the logic on the CPU side to receive 
interrupt messages and send out ACKs, etc.  Somewhat similar to the INTR pin 
on x86 CPUs, but with a lot more functionality.

-- 
John Baldwin <jhb@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org