On Mon, 24 Oct 2011, mark gross wrote: > > > Timeout? why can't we define a proper notification handshake for such > > > things? Timeouts are never right IMO. > > > > > > > I thought that before, but I have come around to the opposite way of thinking > > thanks to some instructive examples from Alan and Rafael. > > > > Some things are simply not visible to the OS. We can expect them to be > > happening but we cannot be sure and there is no clear signal that they aren't > > actually happening. So we need a timeout. > > um > > - USB cannot (I think) know which USB device triggered a wake-from-suspend, > > and in any case cannot directly ask the device why it woke from suspend. > > It has to wait for the device to tell it (in response to a regular > > 'interrupt' poll I assume - but it isn't guaranteed to be reported on the > > first poll) - or timeout and give up waiting. > maybe if you are unwilling to change the user mode stack that is reading > these events. But if you where they you shouldn't need time outs. Remember, here we are talking about timeouts in the kernel stack, not in the user-mode stack. So consider this theoretical situation (which is not very different from reality): The system gets a wakeup signal. Sometime in the next 30 ms or less, there may or may not be an input event -- the kernel has no way to tell other than wait and see. The kernel could simply go right back to sleep without waiting, but if it does and there is a pending input event, then very quickly it will get another wakeup signal, and it'll be right back where it started -- trying to decide whether to stay awake for the next 30 ms. Can you suggest a way to handle this other than using a timeout? Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/linux-pm
