On Saturday, 8 of March 2008, Alan Stern wrote: > This idea just occurred to me. It may or may not end up being useful, > and I don't have any specific applications in mind yet. > > System sleeps are supposed to be transparent to userspace. An I/O > request submitted just before the sleep starts should be blocked until > after the system wakes up. > > Without the freezer to do this blocking for them, drivers will have to > do it themselves. So when a driver is about to carry out an I/O > operation, it has to insure that the operation is mutually exclusive > with sleeping. > > One way to do this is by a private mutex, which would protect both the > block of code doing the I/O and the suspend routine. One for each > device; that's a lot of new mutexes. > > 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. ;-) 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. Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
