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Date: Sun, 26 Mar 2000 12:48:42 -0800 (PST)
From: Matthew Dillon <dillon@apollo.backplane.com>
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To: Nikolai Saoukh <nms@otdel-1.org>
Cc: freebsd-current@FreeBSD.ORG
Subject: Re: Is there spinlocks/semaphores available for drivers?
References: <20000326223650.A17200@Draculina.otdel-1.org> <200003261920.LAA32887@apollo.backplane.com> <20000327003157.A17420@Draculina.otdel-1.org>
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:I do not expect implementation right now.
:I can put some stubs in pertinent places.
:What I am looking for is some kind of
:guidelines/hints/...

    The answer is.... nobody knows yet :-).

    Interrupts will probably wind up running each in its own thread, and
    we will probably adopt the BSDI hybridized model (which runs an interrupt
    synchronously if possible and spools it to a thread otherwise) to 
    increase efficiency.

    I outlined a way to keep the current spl/cpl mechanisms intact while
    at the same time moving interrupts to a threading model in my SMP 
    document:

	http://www.backplane.com/FreeBSD4/
	http://www.backplane.com/FreeBSD4/smp-api.html

    The mechanism I outline will allow interrupt execution concurrent 
    with supervisor execution, and allow interrupt execution concurrent 
    with other interrupts.  For example, two different ethernet interrupts 
    could be taken concurrently with only minor spinlock controls 
    on the IF queue, and both could run concurrent with the TCP stack
    (outside of the spl*() protected areas of the TCP stack).

    The cool thing is that we can make the above work without gutting the
    current spl*() mechanisms.  Frankly, the moment we can take an ethernet
    interrupt concurrent with the network stack, we win.  The moment we can
    take multiple concurrent ethernet interrupts, we win even more.

					-Matt
					Matthew Dillon 
					<dillon@backplane.com>


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