On Fri, 27 Jul 2012, Rusty Russell wrote:
> On Wed, 25 Jul 2012 18:30:41 +0200 (CEST), Thomas Gleixner
> <t...@linutronix.de> wrote:
> > The problem with the current notifiers is, that we only have ordering
> > for a few specific callbacks, but we don't have the faintest idea in
> > which order all other random stuff is brought up and torn down.
> >
> > So I started experimenting with the following:
> >
> > struct hotplug_event {
> > int (*bring_up)(unsigned int cpu);
> > int (*tear_down)(unsigned int cpu);
> > };
> >
> > enum hotplug_events {
> > CPU_HOTPLUG_START,
> > CPU_HOTPLUG_CREATE_THREADS,
> > CPU_HOTPLUG_INIT_TIMERS,
> > ...
> > CPU_HOTPLUG_KICK_CPU,
> > ...
> > CPU_HOTPLUG_START_THREADS,
> > ...
> > CPU_HOTPLUG_SET_ONLINE,
> > ...
> > CPU_HOTPLUG_MAX_EVENTS,
> > };
>
> This looks awfully like hardcoded a list of calls, without the
> readability :)
I'd love to make it a list of calls, though we have module users of
cpu hotplug which makes a list of calls a tad hard.
> OK, I finally got off my ass and looked at the different users of cpu
> hotplug. Some are just doing crazy stuff, but most seem to fall into
> two types:
>
> 1) Hardware-style cpu callbacks (CPU_UP_PREPARE & CPU_DEAD)
> 2) Live cpu callbacks (CPU_ONLINE & CPU_DOWN_PREPARE)
>
> I think this is what Srivatsa was referring to with "physical" and
> "logical" parts. Maybe we should explicitly split them, with the idea
> that we'd automatically call the other one if we hit an error.
>
> struct cpu_hotplug_physical {
> int (*coming)(unsigned int cpu);
> void (*gone)(unsigned int cpu);
> };
>
> struct cpu_hotplug_logical {
> void (*arrived)(unsigned int cpu);
> int (*going)(unsigned int cpu);
> };
>
> Several of the live cpu callbacks seem racy to me, since we could be
> running userspace tasks before CPU_ONLINE. It'd be nice to fix this,
> too.
Yes, I know. I wan't to change that as well. The trick here is that we
can schedule per cpu stuff on a not fully online cpu and only when all
the callbacks have been executed allow user space tasks to be
scheduled on that newly online cpu.
Thanks,
tglx
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