From owner-freebsd-smp  Fri Jun 23 11:37:10 2000
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Date: Fri, 23 Jun 2000 11:37:03 -0700 (PDT)
From: Matthew Dillon <dillon@apollo.backplane.com>
Message-Id: <200006231837.LAA11456@apollo.backplane.com>
To: freebsd-smp@freebsd.org
Subject: Stepping on Toes
Sender: owner-freebsd-smp@FreeBSD.ORG
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    Hmm.  Well, apparently I've stepped on a few toes by not using the
    BSDI mutex code verbatim.

    My position is this:

	* I don't think we can use the BSDI mutex code verbatim
	  because we intend to keep legacy SPL support and it would take
	  as much work addressing that in the BSDI mutex code as it would
	  doing a new core-mutex piece from scratch.

	* I think we CAN use the *WITNESS* code pretty much verbatim.  The
	  reason it isn't in patch set #1 is because the witness code is 
	  not going to be useful until we start unwinding the SPL code in
	  the system, and that is not going to happen until *after* heavy
	  weight interrupt threads are implemented.  Until that time
	  (maybe a month or two from now?) it's just extra baggage.
	  It's the next logical step to take after the heavy weight 
	  interrupt code is made to work, not before.

	  The witness code isn't going to help us for just the Sched and
	  Giant mutexes... simple KASSERT's deal with those situations.

    In regards to the general project.  If people want to try to port 
    the BSDI mutex code directly then be my guest.  I've got a patch set
    that works now ... I can successfully make buildworld on an SP machine
    with it.  You can try porting the BSDI mutex code with or without the
    patchset I've already got, but if after a month or two if you still don't
    have something that works I would recommend going back to the piecemeal
    approach I have taken, starting with my patchset.  

    I won't be angry or anything if people decide to take this course,
    even though I think it's the wrong course to take.  But you guys have
    to decide what to do ASAP.

						-Matt



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