2010/5/18 Rafael J. Wysocki <rjw@xxxxxxx>: > On Tuesday 18 May 2010, Arve Hjønnevåg wrote: >> 2010/5/17 Rafael J. Wysocki <rjw@xxxxxxx>: >> > On Monday 17 May 2010, Arve Hjønnevåg wrote: >> >> 2010/5/14 Rafael J. Wysocki <rjw@xxxxxxx>: >> >> > On Friday 14 May 2010, Arve Hjønnevåg wrote: >> >> >> This patch series adds a suspend-block api that provides the same >> >> >> functionality as the android wakelock api. This version has some >> >> >> changes from, or requested by, Rafael. The most notable changes are: >> >> >> - DEFINE_SUSPEND_BLOCKER and suspend_blocker_register have been added >> >> >> for statically allocated suspend blockers. >> >> >> - suspend_blocker_destroy is now called suspend_blocker_unregister >> >> >> - The user space mandatory _INIT ioctl has been replaced with an >> >> >> optional _SET_NAME ioctl. >> >> >> >> >> >> I kept the ack and reviewed by tags on two of the patches even though >> >> >> there were a few cosmetic changes. >> >> > >> >> > Thanks for the patches, I think they are in a pretty good shape now. >> >> > >> >> > That said, I'd like the changelogs to be a bit more descriptive, at least for >> >> > patch [1/8]. I think it should explain (in a few words) what the purpose of >> >> > the feature is and what problems it solves that generally a combination of >> >> > runtime PM and cpuidle is not suitable for in your opinion. IOW, why you >> >> > think we need that feature. >> >> > >> >> >> >> How about: >> >> >> >> PM: Add opportunistic suspend support. >> > >> > "PM: Opportunistic suspend support" would be sufficient IMO. >> > >> > Now, I'd start with the motivation. Like "Power management features present >> > in the current mainline kernel are insufficient to get maximum possible energy >> > savings on some platforms, such as Android, because ..." (here go explanations >> > why this is the case in your opinion). >> > >> > Next, "To allow Android and similar platforms to save more energy than they >> > currently can save using the mainline kernel, introduce a mechanism by which >> > the system is automatically suspended (i.e. put into a system-wide sleep state) >> > whenever it's not doing useful work, called opportunistic suspend". >> > >> > "For this purpose introduce the suspend blockers framework allowing the >> > kernel's power management subsystem to decide when it is desirable to suspend >> > the system (i.e. when useful work is not being done). Add an API that ..." >> > >> >> PM: Opportunistic suspend support. >> >> Power management features present in the current mainline kernel are >> insufficient to get maximum possible energy savings on some platforms, >> such as Android, because low power states can only safely be entered >> from idle. > > Do you mean CPU low-power states or system low-power states here? > I think either. > I'd add more details here, because it may not be completely clear to the > (interested) reader why entering these states only from idle affects the > possibility to achieve maximum energy savings. I _guess_ you mean that > using idle is not sufficient, because there are so many wakeups on the > systems in question that more savings are still possible. Is that correct? > Yes, is this not what the next paragraph explains? >> Suspend, in its current form, cannot be used, since wakeup >> events that occur right after initiating suspend will not be processed >> until another possibly unrelated event wake up the system again. > > I think the word "cannot" is too strong here. I'd say "not suitable" instead I don't think it is too strong, but I can change it. > and I'd say what kind of wakeup events I meant more precisely (there are > events that wake up a CPU from idle and events that wake up the system from > suspend). When I say wakeup events I mean events that do both. Is there another term for this, or should I just add: "since wakeup events (events that wake the CPU from idle and the system from suspend)..." > >> On some systems idle combined with runtime PM can enter the same power >> state as suspend, but periodic wakeups increase the average power >> consumption. Suspending the system also reduces the harm caused by >> apps that never go idle. On other systems suspend can enter a much >> lower power state than idle. >> >> To allow Android and similar platforms to save more energy than they >> currently can save using the mainline kernel, we introduce a mechanism > > Just "introduce" without "we" works too. > >> by which the system is automatically suspended (i.e. put into a >> system-wide sleep state) whenever it's not doing useful work, called >> opportunistic suspend. > > I think we can address the Kevin's comment about "useful" and say "whenever > it's only doing work that can be done later without noticeable effect on > functionality". > >> For this purpose introduce the suspend blockers framework allowing the >> kernel's power management subsystem to decide when it is desirable to >> suspend the system (i.e. when useful work is not being done). Add an > > Perhaps remove the part in parens entirely. > >> API that that drivers can use to block opportunistic suspend. This is >> needed to avoid losing wakeup events that occur right after suspend is >> initiated. >> >> Adds /sys/power/policy that selects the behavior of /sys/power/state. >> After setting the policy to opportunistic, writes to /sys/power/state >> become non-blocking requests that specify which suspend state to enter >> when no suspend blockers are active. A special state, "on", stops the >> process by activating the "main" suspend blocker. > > ... > >> PM: suspend_block: Add driver to access suspend blockers from user-space >> >> Add a misc device, "suspend_blocker", that allows user-space processes >> to block automatic suspend. >> >> Opening this device creates a suspend blocker that can be used by the >> opener to prevent automatic suspend from occurring. There are ioctls >> provided for blocking and unblocking suspend and for giving the >> suspend blocker a meaningful name. Closing the device special file >> causes the suspend blocker to be destroyed. >> >> For example, when select or poll indicates that input event are >> available, this interface can be used by user space to block suspend >> before it reads those events. This allows the input driver to release >> its suspend blocker as soon as the event queue is empty. If user space >> could not use a suspend blocker here the input driver would need to >> delay the release of its suspend blocker until it knows (or assumes) >> that user space has finished processing the events. >> >> By careful use of suspend blockers in drivers and user space system >> code, one can arrange for the system to stay awake for extremely short >> periods of time in reaction to events, rapidly returning to a fully >> suspended state. > > That's fine by me. > > Thanks, > Rafael > -- Arve Hjønnevåg _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
