On Saturday, 8 of March 2008, Alan Stern wrote: > On Sat, 8 Mar 2008, Rafael J. Wysocki wrote: > > > > My idea is instead to have the PM core provide a new pair of routines > > > for use by drivers. Something like "thread_not_sleepable()" and > > > "thread_sleepable()". > > > > > > The first routine would be called by a driver before starting to do > > > I/O, while no locks are held. If a sleep transition had already > > > started, the routine would block until the sleep was over. Otherwise, > > > the thread would be marked with a NOT_SLEEPABLE flag until the second > > > routine was called. When the PM core wanted to start a system sleep > > > it would have to check whether any threads were marked NOT_SLEEPABLE, > > > and wait until none of them were. > > > > > > This could make drivers a little simpler. It would mean less code to > > > modify, and it would remove one entry from the messy I/O vs. unbind vs. > > > suspend synchronization problem. > > > > > > Comments? > > > > Well, this is what the current freezer does with respect to kernel threads, > > only the name of the flag is different. ;-) > > They aren't exactly the same, although they certainly are similar. The > difference lies in what happens when a task calls set_freezable() > after a system sleep has begun; its TIF_FREEZE flag doesn't immediately > get set. We can only wait for them at one point, however. Periodic checking if there are no unsleepable tasks around wouldn't be very practical, IMHO. > Also, the current freezer doesn't offer a clear_freezable() routine. Oh, it would be easy to add one. :-) > > You basically need something very similar to the current freezer in order > > to implement the "PM core would have to check whether any threads were marked > > NOT_SLEEPABLE, and wait until none of them were" functionality. > > Another approach would be to use something like an rwsem. Hopefully > without all the cache-line-bouncing overhead on SMP systems. Well, to me, rwsem sounds definitely better. Still, I think it's better to avoid locking it for too long, so we could use a variable protected by the rwsem such that if it's 'true', unsleepable tasks checking it will put themselves into a wait queue which will be woken up by the PM core during resume. Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
