On Thu, 15 Jun 2006, Pavel Machek wrote: > > > > Why? We are saving state to memory, we should not need any other > > > devices to do that. > > > > Hell no, we're not. > > ? We're clearly saving state to _user_ space etc in some cases. That's not "memory", that is "pageable data and processes that can - and do - depend on other devices in ways that the kernel is not necessarily even aware of". Just as the most obvious example, it's entirely possible that when you ask the graphics system to save its state, it might actually tell clients across a network that their window got occluded or something. The same is true of various virtual devices that the kernel may not even know about. Network devices done as tunnels in user space etc. They may _look_ like system devices at the root of the device tree to the kernel, but that's just because the kernel has not a f*cking clue about what they are actually connected to. So we're _not_ just saving data to memory. We're allocating memory (which means that we want to access every single device that may do write-back), and we're calling out to user space (which means that we _really_ don't know what a device may need). > Okay, but graphical console means X these days, and -- being userspace > -- needs special casing, anyway. No it does not. The point is, what I descibe - with a separate "save state but don't disable" - doesn't need any special casing at all, exactly because it doesn't do anythign STUPID. > For fbcon, etc, no, we do not any other devices, so it actually works > okay. Yeah, Linux suspend is generally felt to "work ok". Not. > > In fact, done right, if you know the machine powers off, the final suspend > > should literally not be needed. "Remove power globally" is actually a very > > good suspend/shutdown mechanism that doesn't even need any driver support ;) > > Actually, that's bad idea; some machines are unable to power down with > devices still running. Can you read my sentence again? "If you know the machine powers off"? Trust me, if you remove power from the devices, that machine _will_ power down. It's that simple. It's not "maybe", or "if" or "unable to". It's basic physics. Just removing power can often be the most efficient way to shut down. It's a perfectly fine algorithm, if the user asks you to do that. That doesn't mean that it's always the right thing to do. It's just that it's an option: "save state to disk, then power down, and screw any PCI devices that don't think they know how to do it". Linus
