On Sunday, 20 May 2007 23:06, Oleg Nesterov wrote: > 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?
Ah, sorry, I didn't understand the question correctly. > > 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? Yes, we can do this, I think. > > 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. Yes, that seems reasonable. This means that every user of freezable kernel threads who installs a CPU hotplug notifier will have to assume that its kernel threads are frozen when the notifier is called. Greetings, Rafael - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
