On Thu, 30 Oct 2008, Miklos Szeredi wrote: > On Thu, 30 Oct 2008, Alan Stern wrote: > > On Thu, 30 Oct 2008, Miklos Szeredi wrote: > > > > > On Wed, 29 Oct 2008, Alan Stern wrote: > > > > I discussed this last summer with Rafael. It's a lot harder than it > > > > looks, for all sorts of reasons. For example, what about user tasks > > > > that have access to memory-mapped I/O regions? > > > > > > What about them? Freezing doesn't seem to help with that. > > > > Sure it does. A frozen process can't touch a memory-mapped I/O region, > > whereas a non-frozen process can. > > But it can be in the middle of I/O by your definition. True. Yet another problem... > > Would you like to write a first-pass patch? I don't think it will > > work. > > If somebody doesn't beat me to it, I'll do that (first implemented > with a global rw-sem). Converting it to per-CPU counters later on should be fairly easy. > > Doing that seems like a lot of work, just as modifying every driver > > does. Changing a few kernel entry points is simpler, but I'm pretty > > sure it won't work. For instance, tasks can block arbitrarily long on > > read calls (waiting for data to arrive); you can't allow such things to > > prevent the system from suspending. > > But we already do: either > > a) it's in interruptible sleep (I/O on sockets, pipes, etc), and > freezing simply interrupts it, or > > b) it's in uninterruptible sleep and suspend will wait it out (or > time out). > > In the new scheme we could retain that part of the freezer: interrupt > all tasks which are inside the critical region and wait for them to > exit the critical region. > > To put it in another way: it's still the freezer, it does all the same > things as the old freezer, except that the condition for freezing is > not that the task is out of the kernel, rather that it's out of the > disable_supend - enable_suspend region. As such it's not a big change > to the whole suspend system, and so there shouldn't be anything big > going wrong there. Okay. Don't forget things like ioctl for sockets -- they often involve doing I/O directly to the network interface device. What happens to a task accessing a non-regular file on a fuse filesystem? :-) Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
