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Date:      Thu, 02 May 2002 09:58:06 -0700
From:      Terry Lambert <tlambert2@mindspring.com>
To:        John Baldwin <jhb@FreeBSD.org>
Cc:        Jonathan Mini <mini@freebsd.org>, freebsd-smp@FreeBSD.ORG, Andrew Gallatin <gallatin@cs.duke.edu>
Subject:   Re: hlt when idle?
Message-ID:  <3CD1701E.7F0F4CB4@mindspring.com>
References:  <XFMail.20020502101631.jhb@FreeBSD.org>

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John Baldwin wrote:
> >> So each CPU gets (1/num_cpu) * hz  clock interrupts/sec?
> >
> > Yes, but because the timer is set to num_cpu*hz, each CPU ends up getting
> > the normal hz interrupts. That's why it runs round-robin but looks like a
> > broadcast.
> 
> Eh, are you talking about the Alpha?  On x86 we don't do this and have to use
> IPI's to simulate a broadcast-type deal.

You can get real broadcast behaviour *IF* the clock interrupt
comes directly into the APIC, instead of being cascaded through
the ISA PIC.  That's kind of the whole point: some motherboards
do, some motherboards don't.

-- Terry

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