On 05/20, Rafael J. Wysocki wrote:
>
> On Sunday, 20 May 2007 21:54, Oleg Nesterov wrote:
> >
> > I am a bit afraid of too many yes/no options for the freezer, a couple of naive
> > questions.
> >
> > 1. Can't we make all wqs freezable? I still can't see the reason to have both
> > freezable and not freezable wqs.
>
> The reason might be the same as for having freezable and nonfreezable kernel
> threads in general. For example, there are some kernel threads that we need
> for saving the image and I don't see why there shouldn't be any such
> workqueues.
OK, I see.
> > 2. Why do we need CPU_TASKS_FROZEN? Can't we change cpu-hotplug to always
> > freeze tasks right now, without any additional changes?
>
> In principle, we can, but for this purpose we'd have to modify all NOFREEZE
> tasks.
Why?
> That wouldn't fly, I'm afraid.
>
> > Any subsystem should handle correctly the case when _cpu_down() (say)
> > is called with tasks_frozen == 1 anyway. So, why can't we simplify
> > things and do
> >
> > _cpu_down(int tasks_frozen)
> >
> > if (!tasks_frozen)
> > freeze_processes();
> > ...
> >
> > right now?
>
> But we call _cpu_down() after device_suspend(), so many tasks are already
> frozen at this point. We'd only need to freeze those that are not frozen and
> in _cpu_up() we'd have to thaw them.
Not sure I understand. When we call _cpu_down() after device_suspend(), we
check tasks_frozen == 1, and do not call freeze_processes(). If the task
could be frozen, it is already frozen.
When _cpu_down() sees tasks_frozen = 0, it does freeze_processes() itself,
and thaw_tasks() on return.
IOW, we never send (say) CPU_DEAD, always CPU_DEAD_FROZEN.
Wouldn't fly?
Oleg.
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