Summary: -current will be destabilized for an extended period (on the order
of months).  A tag (not a branch) will be laid down before the initial
checkin, and non-developers should either stick closely to that tag until
the kernel stabilizes, or expect large doses of pain.  This tag will be
laid down as soon as June 26, 00:00 PST, with a minimum 24 hour warning


Last week, approximately 20 BSD developers got together and discussed how
to move FreeBSD's SMP support to the next level.  Our effort will be
largely based on the work that has been done in BSD/OS, which should make
things go much more smoothly than they otherwise might, but we still expect
-current to be destabilized for an extended period of time.

Matthew Dillon is currently working on the locking primitives, as well as
some changes to the way our top-level kernel locking works.  His initial
code will not remove spl()s.  This code will probably be committed as the
first step, as soon as June 26, 00:00 PST, and Peter Wemm will lay a tag
down just beforehand.  We will give at least 24 hours notice before the tag
is laid down.  Be forewarned: if you are doing anything with -current
besides FreeBSD development, you will probably want to stop tracking
-current at that point for a while.

Greg Lehey will be working on the initial cutover to interrupt threads (as
well as the lazy interrupt thread context switching code later on).  spl()s
will go away as soon as interrupt threads start working.  Once interrupt
threads are working, most of the remaining work of threading the kernel
will be able to go on in parallel.

Device driver maintainers will be able to convert device drivers over a
period of several months.  We expect to have a compatibility shim in place
initially, but there will be a hard cutoff date sometime before the release
of FreeBSD 5.0 where the compatibility shim is removed.  Before getting too
excited about this part of the conversion to a threaded kernel, please keep
in mind that 1) there will be plenty of time to do this conversion, 2) the
conversion is pretty trivial for most drivers, and 3) as we get to the
stage where the conversion becomes possible, there will be much more detail
about how to do the conversion, as well as the working examples of the
first drivers to be converted.

The addition of kernel support for scheduler activations is generally a
separate project, but there are some interdependencies between the SMP and
scheduler activations changes, especially in the scheduler and the proc

There are many other SMP-related changes that will be made to the kernel
that are not specifically mentioned in this email, since they are not of
significant interest from a grand overview perspective.  However, there are
many details, and if you want to follow the technical discussions, you will
want to be subscribed to at least the -current and -smp mailing lists.

Finally, here are some notes about the organization of this effort.  I was
cajoled into acting as the manager of this effort.  That doesn't mean I'm
going to do all (or even a major part) of the work; it merely means I'm the
focal point of communications and decisions made with regard to the
project.  Right now, there are at least a dozen highly capable FreeBSD
developers that have taken an interest in working on this project.  We, as
a group, have made a number of decisions about how to attack this project.
If you want to contribute to technical aspects of the project, please jump
in.  However, consider that the general direction we're taking with the SMP
effort is the result of a number of very knowledgeable people hashing this
out over a period of two days; don't expect that direction to change in the
short-term.  So, if you have grievances about the way this project is being
run, complain to me, but please let the other developers work on this in
relative peace.


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