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Date:      Wed, 19 Apr 2000 17:56:01 -0400 (EDT)
From:      Andrew Gallatin <gallatin@cs.duke.edu>
To:        freebsd-smp@freebsd.org
Subject:   I/O APIC
Message-ID:  <14590.10426.763064.533504@grasshopper.cs.duke.edu>

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This is probably a dumb question, so forgive me.  My low-level system
knowledge is pretty much limited to alphas & I don't know a lot about
PCs. 

When installing Solaris/x86 on one of our PowerEdge 2400s (SMP
capable, 2 I/O APICs, 1 CPU), I noticed that it uses the I/O APICs for
interrupts rather than the normal isa irq x.  Is there an advantage to
this?

This rang a bell, because the same PowerEdge2400 tends to spew 'stray
irq 15' when under heavy interrupt load & running FreeBSD.  There's
nothing attached to irq 15.  I'm thinking that the traditional irq
method is probably not well tested on this hardware since it would
seem that at least some OSes use the I/O APIC even in single CPU mode.

Would it be better for FreeBSD run I/O APIC capable machines via the
I/O APIC even when using only a single CPU? I know we can't do this
now, but would it be worth sorting through that code?  Is there more
to it than untangling the IOAPIC and SMP ifdefs?

Again, apologies for the dumb question.

------------------------------------------------------------------------------
Andrew Gallatin, Sr Systems Programmer	http://www.cs.duke.edu/~gallatin
Duke University				Email: gallatin@cs.duke.edu
Department of Computer Science		Phone: (919) 660-6590




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