Re: 2.7 thoughts

[William Lee Irwin III <wli@holomorphy.com>]

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.

On Fri, Oct 10, 2003 at 11:03:20AM -0700, Tim Hockin wrote:
> 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.

I think there is some generalized cpu hotplug stuff that's gone in that
direction already, though I don't know any details. The bits about non-
cooperative offlining were very interesting to hear, though.

-- wli