Understanding the Characteristics of Android Wear OS. Renju Liu and Felix Xiaozhu Lin Purdue ECE

Transcription

1 Understanding the Characteristics of Android Wear OS Renju Liu and Felix Xiaozhu Lin Purdue ECE

2 The Wearable stack 5

3 Top questions Wearables should enjoy Baremetal performance Baremetal efficiency In this talk: Android Wear Are we close to baremetal? What is going on inside? How should the OS evolve? 6

4 Observation -- Symptoms The current performance & efficiency are far from baremetal Pacing inefficient face update: 400ms 88% busy Clock face update 7

5 Observation -- Symptoms The current performance & efficiency are far from baremetal Launch settings Pacing inefficient face update: 400ms 88% busy Racing slow Launch an in-mem app: 1 sec 9

6 What happens underneath? User touch Launch action starts App UI shown 177 ms 810 ms 11

7 What happens underneath? User touch Launch action starts App UI shown Power / mw ms 810 ms 12

8 What happens underneath? Power / mw User Launch action touch starts Phase 1 Phase 2 App UI shown CPU Exec. Idle Busy with various tasks 177 ms 810 ms 13

9 What happens underneath? Power / mw User Launch action touch starts Phase 1 Phase 2 App UI shown CPU Exec. Idle Busy with various tasks 177 ms 810 ms 28 ms 130 ms 19 ms 14

10 Four Aspects CPU busy?? Thread-level parallelism () Microarchitectural behaviors Won t talk about our methodologies 20

11 Profiling Core Use Scenarios Wakeup Update notification wrist Single Input launch apps palming voice Sensing Accel heart baro Interaction Game notes navigation 21

12 OS execution dominates CPU usage. 100% 75% 50% 25% 0% update notif wrist touch lch.set lch.calc lch.game palming voice game notes navi accel heart baro Wakeup Single In. Interact. Sensing 26

13 OS execution dominates CPU usage. 100% OS:Clockwork OS:daemons 75% 50% 25% 0% update notif wrist touch lch.set lch.calc lch.game palming voice game notes navi accel heart baro Wakeup Single In. Interact. Sensing 27

14 OS execution dominates CPU usage. 100% Apps OS:Clockwork OS:daemons 75% 50% 25% 0% update notif wrist touch lch.set lch.calc lch.game palming voice game notes navi accel heart baro Wakeup Single In. Interact. Sensing 28

15 OS execution dominates CPU usage. 100% Idle Apps OS:Clockwork OS:daemons 75% 50% 25% 0% update notif wrist touch lch.set lch.calc lch.game palming voice game notes navi accel heart baro Wakeup Single In. Interact. Sensing 29

16 OS execution dominates CPU usage. 100% Idle Apps OS:Clockwork OS:daemons 75% 50% 25% 0% update notif wrist touch lch.set lch.calc lch.game palming voice game notes navi accel heart baro Wakeup Single In. Interact. Sensing 30

17 OS execution dominates CPU usage. 31

18 OS execution dominates CPU usage. 32

19 Costly OS services are... 33

20 Costly OS services are likely cruft. 34

21 Hot functions: highly skewed distribution Top 5 à >20% CPU cycles Top 50 à >50% CPU cycles 35

22 Hot functions: highly skewed distribution Top 5 à >20% CPU cycles Top 50 à >50% CPU cycles Manipulating basic data structures Legacy/improper OS designs 36

23 Hot functions: highly skewed distribution Top 5 à >20% CPU cycles Top 50 à >50% CPU cycles Manipulating basic data structures Legacy/improper OS designs 37

24 Idle episodes: plentiful and of various lengths Time (ms) Pct. Overall Episodes Pct. Explained % % notes % % voice % % lch.game % % lch.calc % % lch.set % % touch % % update % % navi % % notif 38

25 Idle anomalies are caused by Device suspend Voice UI Cont. interaction Cont. interact.+neti/o Storage I/O User think Bluetooth tail time OS shell policy App policy notes lch.game lch.set update navi notif Time / ms Time (ms) Pct. Overall Episodes Pct. Explained % % notes % % voice % % lch.game % % lch.calc % % lch.set % % touch % % update % % navi % % notif 39

26 Idle anomalies are caused by Device suspend Voice UI Cont. interaction Cont. interact.+neti/o Storage I/O User think Bluetooth tail time OS shell policy App policy notes lch.game lch.set update navi notif Time / ms Time (ms) Pct. Overall Episodes Pct. Explained % % notes % % voice % % lch.game % % lch.calc % % lch.set % % touch % % update % % navi % % notif Legacy/improper OS designs Performance overprovisioning 40

27 Substantial on a par with desktop # of concurrent threads 42

28 Substantial on a par with desktop # of concurrent threads 43

29 Substantial on a par with desktop : avg. busy CPU cores (over non-idle time) # of concurrent threads 44

30 due to short interactions. : avg. busy CPU cores (over non-idle time) # of concurrent threads 45

31 Apps are mostly single-threaded; OS contributes to significantly. 46

32 Wearable suffers from inefficiency Cycles-per-instruction (lower is better) (high!) 47

33 Wearable suffers from inefficiency Cycles-per-instruction (lower is better) (high!) Smartphone as a comparison web rendering <2 SPEC INT 48

34 Wearable suffers from inefficiency Cycles-per-instruction (lower is better) (high!) Smartphone as a comparison web rendering <2 SPEC INT 49

35 Wearable suffers from inefficiency Cycles-per-instruction (lower is better) (high!) Smartphone as a comparison web rendering <2 SPEC INT 50

36 The major cause: complex OS code (L1 icache, itlb, and branch predictor) 51

37 The major cause: complex OS code (L1 icache, itlb, and branch predictor) problem will NOT be gone with future wearable CPUs 52

38 Four Aspects CPU busy OS dominates Lots of cruft Skewed hot functions Legacy bottlenecks Anomalous OS flaws Too much performance Thread-level parallelism Desktop-like OS-contributed Microarchitectural behaviors Mismatch OS code complexity 54

39 Repair, don t overhaul (yet) CPU busy OS dominates Lots of cruft Skewed hot functions Legacy bottlenecks Anomalous OS flaws Too much performance Thread-level parallelism Desktop-like OS-contributed Microarchitectural behaviors Mismatch OS code complexity 55

40 How about after that? (i.e. next-gen wearable OS ) We probably will reach a point when OS overhaul/redesign is justified. Specializing OS for common, single-app scenarios 56

41 Restructuring OS for Wearable Specializing OS for common, single-app scenarios OS Daemons Full Simple Activity Manager Full Simple Window Manager Kernel 58

42 Restructuring OS for Wearable OS Daemons Apps Full Simple Activity Manager Full Simple Window Manager Kernel 59

43 Restructuring OS for Wearable OS Daemons Apps Simple Full Activity Manager Simple Full Window Manager Kernel 60

44 Final takeaway Wearables: unique usage and hardware Many mobile OS tradeoffs are invalid efficiency v.s. flexibility & programming ease Immediate actions: fixing individual OS components Future: OS specialization may be needed Tools, data, and benchmark videos xsel.rocks/p/wear 66

45 FAQ You forgot Apple Watch or Samsung Tizen. Isn t your discovery just some oversight of Google engineers? Aren t these things easy to fix? Doesn t multicore wearable sound crazy? Power! I want to learn about power. I bet the Android Wear team already fixed these! xsel.rocks/p/wear 67

46 Has Android Wear improved? 68

47 69