On Wednesday 26 May 2010, Matthew Garrett wrote: > On Wed, May 26, 2010 at 02:57:45PM +0200, Peter Zijlstra wrote: > > > I fail to see why. In both cases the woken userspace will contact a > > central governing task, either the kernel or the userspace suspend > > manager, and inform it there is work to be done, and please don't > > suspend now. > > Thinking about this, you're right - we don't have to wait, but that does > result in another problem. Imagine we get two wakeup events > approximately simultaneously. In the kernel-level universe the kernel > knows when both have been handled. In the user-level universe, we may > have one task schedule, bump the count, handle the event, drop the count > and then we attempt a suspend again because the second event handler > hasn't had an opportunity to run yet. We'll then attempt a suspend and > immediately bounce back up. That's kind of wasteful, although it'd be > somewhat mitigated by checking that right at the top of suspend entry > and returning -EAGAIN or similar. I still think it would cause a loop-alike behavior between the user space power manager and the kernel PM core to happen, because the power manager will always have to check the user space counter after a failing suspend attempt. Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
