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. Also, the current freezer doesn't offer a clear_freezable() routine. > 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. Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
