Re: [PATCH 3/4] 2.6.2-rc2-mm2 CPU Hotplug: The Core

[Rusty Russell <rusty@rustcorp.com.au>]

In message <20040202154040.GA5895@elte.hu> you write:
> user-space tasks that rely on running on a specific CPU need a callback
> too. (probably in the form of a signal, which, if unhandled, terminates
> the task.) Eg. if a webserver has a mode to run one thread per CPU, then
> the server needs to adapt to the new situation when a CPU goes away. We
> cannot just unilaterally migrate a task and violate its affinity.

Well, that's what we'd do anyway, to deliver the signal.

This terminating signal idea is simply flawed: affinity is inherited,
so you're killing a process which knows nothing anyway.

If we can't do it well, leave it to userspace to sort out 8)

> another thing: if the migrate-irqs op is done atomically too (together
> with the migrate-tasks op) then the special-cases in idle_balance() and
> rebalance_tick() could go away too.

Exactly.  It simplifies a number of things.

Thanks,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.