On Mon, May 31, 2010 at 3:05 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > On Monday 31 May 2010, Neil Brown wrote: >> On Thu, 27 May 2010 23:40:29 +0200 (CEST) >> Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: >> >> > On Thu, 27 May 2010, Rafael J. Wysocki wrote: >> > >> > > On Thursday 27 May 2010, Thomas Gleixner wrote: >> > > > On Thu, 27 May 2010, Alan Stern wrote: >> > > > >> > > > > On Thu, 27 May 2010, Felipe Balbi wrote: >> > > > > >> > > > > > On Thu, May 27, 2010 at 05:06:23PM +0200, ext Alan Stern wrote: >> > > > > > >If people don't mind, here is a greatly simplified summary of the >> > > > > > >comments and objections I have seen so far on this thread: >> > > > > > > >> > > > > > > The in-kernel suspend blocker implementation is okay, even >> > > > > > > beneficial. >> > > > > > >> > > > > > I disagree here. I believe expressing that as QoS is much better. Let >> > > > > > the kernel decide which power state is better as long as I can say I >> > > > > > need 100us IRQ latency or 100ms wakeup latency. >> > > > > >> > > > > Does this mean you believe "echo mem >/sys/power/state" is bad and >> > > > > should be removed? Or "echo disk >/sys/power/state"? They pay no >> > > > >> > > > mem should be replaced by an idle suspend to ram mechanism >> > > >> > > Well, what about when I want the machine to suspend _regardless_ of whether >> > > or not it's idle at the moment? That actually happens quite often to me. :-) >> > >> > Fair enough. Let's agree on a non ambigous terminology then: >> > >> > forced: >> > >> > suspend which you enforce via user interaction, which >> > also implies that you risk losing wakeups depending on >> > the hardware properties >> >> Reasonable definition I think. However the current implementation doesn't >> exactly match it. >> With the current implementation you risk losing wakeups *independent* of the >> hardware properties. > > Define "losing", please. > > Currently, we simply don't regard hardware signals occuring _during_ the > suspend operation itself as wakeups (unless they are wakeup interrupts to be > precise, because these _are_ taken into account by our current code). > > The reason is that the meaning of given event may be _different_ at run time > and after the system has been suspended. For example, consider a power button > on a PC box. If it's pressed at run time, it usually means "power off the > system" to the kernel. After the system has been suspended, however, it means > "wake up". So, you have to switch from one interpretation of the event to the > other and that's not an atomic operaition (to put it lightly). > >> Even with ideal hardware events can be lost - by which I mean that they will >> not be seen until some other event effects a wake-up. >> e.g. the interrupt which signals the event happens immediately before the >> suspend is requested (or maybe at the same time as), but the process which >> needs to handle the event doesn't get a chance to see it before the suspend >> procedure freezes that process, and even if it did it would have no way to >> abort the suspend. >> >> So I submit that the current implementation doesn't match your description of >> "forced", is therefore buggy, and that if it were fixed, that would be >> sufficient to meet the immediate needs of android. > > I don't really think it may be fixed with respect to every possible kind of > hardware. On platforms where I/O interrupts are wakeup events it should > work right now. On other platforms it may be impossible to overcome hardware > limitations. > There is no reason you cannot make the rtc alarms work reliably on x86 hardware. Even if you may loose key events while suspending I think it is still valuable to have reliable alarms. I gave an example earlier why reliable alarms are useful (dvr application). -- Arve Hjønnevåg -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
