Re: 2.7 thoughts

[Tim Hockin <thockin@hockin.org>]

On Fri, Oct 10, 2003 at 07:47:23AM -0700, William Lee Irwin III wrote:
> You need at least enough warning to get out of critical sections (e.g.
> holding a spinlock) and dump registers out to memory. i.e. as long as it
> takes to schedule out whatever's currently running on the thing.

I've got a patch against RedHat's 2.4.x kernel with some version of O(1)
scheduler that migrates all processes off a CPU and makes it ineleigible to
run new tasks.  When the syscall returns, it is safe to remove the CPU.
Processes that are running or sleeping and can be migrated elsewhere are
migrated.  Running processes that have set_cpus_allowed to ONLY the
processor in question are marked TASK_UNRUNNABLE and moved off the runqueue.
Sleeping processes that have set_cpus_allowed to ONLY the processor in
question are left unmolested until they wake up, at which point they will be
marked UNRUNNABLE.

It was done to allow software to bring CPUs on/offline, but it should work
for this.  IRQs not done yet, either.

-- 
Notice that as computers are becoming easier and easier to use,
suddenly there's a big market for "Dummies" books.  Cause and effect,
or merely an ironic juxtaposition of unrelated facts?