Energy Performance and Accounting in Mobile Operating Systems

Transcription

1 Computer Laboratory Energy Performance and Accounting in Mobile Operating Systems James Snee and Andrew Rice 1

2 Too many features not enough energy... 2

3 Where is the energy spent?? 3

4 Power (Watts) What is the phone doing? Seconds (s) 4

5 Even the idle state of the device is unpredictable Patterns exist Power (Watts) High variance in power consumption Seconds (s) 5

6 Frequency Density Changes in the OS can have profound effects Joules Andrew Rice, Simon Hay, Measuring mobile phone energy consumption for wireless networking, Pervasive and Mobile Computing, Volume 6, Issue 6, December 2010, Pages

7 Power (Watts) Android 1.1 checks that no one is using the same IP address Time (seconds) Andrew Rice, Simon Hay, Measuring mobile phone energy consumption for wireless networking, Pervasive and Mobile Computing, Volume 6, Issue 6, December 2010, Pages

8 Power (Watts) Android 2.1 doesn t bother checking... Time (seconds) Andrew Rice, Simon Hay, Measuring mobile phone energy consumption for wireless networking, Pervasive and Mobile Computing, Volume 6, Issue 6, December 2010, Pages

9 Consumption difference found by monitoring the network Some effects not visible outside the device 9

10 What s going on inside the device? We instrument Android s Linux Kernel Applications Middleware / Services Native interfaces Linux Kernel 10

11 We are able to make use of existing profiling tools KProbes DTrace Perf SystemTap FTrace Valgrind OProfile Linux Trace Toolkit 11

12 We are able to make use of existing profiling tools KProbes DTrace Perf SystemTap FTrace Valgrind OProfile Linux Trace Toolkit 12

13 Power (Watts) We logged every system call made during idle test using FTrace Seconds (s) 13

14 FTrace places instrumentation in every system function Adds a call to the mcount routine in the prelude of every function (mcount: arch/arm/kernel/entry-common.s) This routine stores tracing information into a small ring-buffer Requires a rooted device and a custom built kernel 14

15 Example FTrace (function tracer) trace output [Process Name] [CPU] [Time since boot]: [function] <- [parent] : fsnotify_parent <-vfs_write : fsnotify <-vfs_write : srcu_read_lock <-fsnotify : srcu_read_unlock <-fsnotify : sys_dup2 <-ret_fast_syscall : sys_dup3 <-sys_dup : expand_files <-sys_dup : filp_close <-sys_dup : locks_remove_posix <-filp_close : fput <-filp_close : fsnotify_parent <-fput : fsnotify <-fput : locks_remove_flock <-fput : module_put <-fput : put_pid <-fput : file_sb_list_del <-fput : files_lglock_local_unlock_cpu <-file_sb_list_del : drop_file_write_access <-fput : mnt_drop_write <-drop_file_write_access : call_rcu <-fput 15

16 Annotated the first 1ms of the idle trace Power (Watts) 1ms Seconds (s) 16

17 Too much noise in the data Power sampled at 10kHz 17

18 Instrument individual functions with SystemTap Applications Middleware / Services Native interfaces ST ST Linux Kernel ST ST FTrace 18

19 SystemTap instruments the Kernel without the need to recompile Tap Script Translate to C Insert and run Build Kernel Module Report back the internal state of functions Safer interface to kprobes, no more panics 19

20 consumed per kilobyte (J) Energy Energy consumed per kilobyte (J) WiFi + TCP energy consumption appears to follow a trend Message size (kb) Message Size (kb) Andrew Rice, Simon Hay, Measuring mobile phone energy consumption for wireless networking, Pervasive and Mobile Computing, Volume 6, Issue 6, December 2010, Pages

21 Energy consumed per kilobyte (J) We re using SystemTap to investigate these outliers Message Size (kb) What s going on inside TCP? Andrew Rice, Simon Hay, Measuring mobile phone energy consumption for wireless networking, Pervasive and Mobile Computing, Volume 6, Issue 6, December 2010, Pages

22 We are using SystemTap to instrument the Linux TCP implementation probe printf("tcp %ul %s>%s \n",gettimeofday_s(),thread_indent(1),probefunc()) } 22

23 Moving instrumentation into the OS is giving us a better picture of what s going on 23

24 Computer Laboratory Energy Performance and Accounting in Mobile Operating Systems James Snee and Andrew Rice Portions of this page are reproduced from work created and shared by Google and used according to terms described in the Creative Commons 3.0 Attribution License. 24