On Tuesday, 31 July 2007 12:02, Pavel Machek wrote: > On Tue 2007-07-31 12:08:40, Rafael J. Wysocki wrote: > > On Tuesday, 31 July 2007 11:39, Rafael J. Wysocki wrote: > > > Hi, > > > > > > On Tuesday, 31 July 2007 10:01, Pavel Machek wrote: > > > > Hi! > > > > > > > > > > > refrigerator_called is only reset after try_to_freeze_tasks() has found it > > > > > > > equal to one. There is only a small window between checking it in > > > > > > > wait_event_timeout() and resetting it, > > > > > > > > > > > > Yes. > > > > > > > > > > > > > but then we go to send freeze requests > > > > > > > to the remaining tasks and we count 'todo' from the start, so that shouldn't > > > > > > > be a problem. > > > > > > > > > > > > ... and we find the task which is not frozen() yet, but which has already passed > > > > > > the "set condition and wakeup", increment todo, and wait for the event. If it was > > > > > > the last task, we will sleep until timeout. > > > > > > > > > > > > I agree, this is not fatal and unlikely, but still it is a race. I think it is > > > > > > better to move this code down, after frozen_process(). > > > > > > > > > > OK, I see your point. The updated patch is appended. > > > > > > > > > > > (offtopic: strictly speaking, we don't even need the "refrigerator_called", we > > > > > > only need the wait_queue_head_t. try_to_freeze_tasks() just adds the "current" > > > > > > to wq at the very start of the main loop). > > > > > > > > > > Hmm, yes, I think so. > > > > > > > > Ok, could we just do schedule_timeout(HZ/10) or something, but when we > > > > _know_ we woke someone, wakeup() that task? No new variables, keep > > > > existing logic. > > > > > > The logic doesn't change that much. :-) > > > > > > > That should still get most of the benefits, and be two liner, no? > > > > > > Well, I think we can avoid using refrigerator_called, if this is a problem, but > > > the patch won't be a two liner. > > > > To be precise, we'd need to add current to the wait queue manually, which > > would require us to open code wait_event_timeout(), more or less. > > > > Still, maybe to many things are done in this patch at a time. I'll try to > > split it into smaller steps. :-) > > Ok, whatever. > > Hmm, you could be sneaky and send signals to refrigerator, that should > trigger early return from schedule_timeout()... Hmm, did you mean *from* the refrigerator? > <runs away, hides> Well, that wasn't really necessary. ;-) The three patches in the next messages are functionally equivalent to this one. They do the following: * make try_to_freeze_tasks() wait instead of busy looping * make try_to_freeze_tasks() measure the time it takes to freeze tasks * replace the timeout with counting "waits" Greetings, Rafael -- "Premature optimization is the root of all evil." - Donald Knuth _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
