Mobile/Powersaving/Wakeups

Overview

'Wakeups' are instances where a thread enters activity. Each such wakeup stops the CPU from sleeping. Several short wakeups are much worse than a single long wakeup, because each wakeup will prevent sleeping for a short time afterwards, and sleeping can save a lot of power (see powertop docs). So avoiding wakeups is important, and if they are unavoidable then 'clumping' them together is preferable to scattering them at semi-random times.

Some Wakeups of Note

• nsIdleService::IdleTimerCallback (~1/5 seconds) - bug 564118 (waiting to land)
• nsUITimerCallback (1/5 seconds) - bug 508518
• xpcom/ds/nsExpirationTracker.h:321
• netwerk/protocol/http/nsHttpHandler.cpp:376
• xpcom/ds/nsRecyclingAllocator.cpp:235 (hundreds of seconds?)

Old data, uncertain:

• xpcom/reflect/xptcall/src/md/unix/xptcstubs_gcc_x86_unix.cpp:101 - likely some JS callbacks (~1/5 seconds)
• The TileManager code sets and attribute each time we paint, which causes the Refresh Driver to spring into action, and stay active for a few frames at 50Hz. As a result on pages with enough animations - even slow ones - the Refresh Driver timer constantly or almost constantly runs at 50Hz. This effectively nullifies the benefits of timer grouping/clumping, and ironically exactly in the case where that would have helped (lots of animations). But, the TileManager will be replaced by new Layers code, so hopefully this will be a thing of the past.

Other wakeups to investigate:

• SMIL SVG animation runs at a 20ms (50fps) timer, no matter what the animation
• nsHttpConnectionMgr::OnMsgPruneDeadConnections (http keepalive stuff)

Things to Investigate

• SetWaitableTimerEx in Windows 7 might help the OS group Gecko's timers with other timers running. Do other OSes have similar things?

Debugging/Finding Wakeups

Mobile/Powersaving/Wakeups/Debugging