Messages in this thread | | | Subject | Re: [PATCH 1/1] hotplug cpu: migrate a task within its cpuset | From | Rusty Russell <> | Date | Mon, 27 Aug 2007 17:01:34 +1000 |
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On Sun, 2007-08-26 at 01:09 -0700, Andrew Morton wrote: > On Sun, 26 Aug 2007 10:47:24 +1000 Rusty Russell <rusty@rustcorp.com.au> wrote: > > Userspace is not monolithic. If you refuse to take a CPU offline > > because a task is affine, then any user can prevent a CPU from going > > offline. > > That's a kernel bug.
You mean "would be if it were implemented"? Although consider the equivalent forkbomb or thrashing userspace problems, where we just say "use quotas".
Just to clarify: that is not how we work, we migrate tasks off a dying CPU, breaking affinity and printing a warning if necessary.
It was simple and has not proven problematic in practice. (Userspace cpu affinity has been a question of optimality not correctness)
> > You could, perhaps, introduce a "gentle" offline which fails if process > > affinity can no longer be met. > > Suitably privileged userspace should be able to > > 1) prevent tasks from binding to CPU N then > 2) migrate all tasks which can use CPU N over to other CPU(s) then > 3) offline CPU N.
Indeed, (1) is missing. I would hesitate to introduce more infrastructure in an under-worn and over-buggy part of the kernel though.
Rusty.
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