Energy Performance and Accounting in Mobile Operating Systems

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Energy Performance and Accounting in

Mobile Operating Systems

James Snee and

Andrew Rice

Computer Laboratory

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Too many features not enough energy...

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Where is the energy spent?

?

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What is the phone doing? Seconds (s) Po w e r (W a tt s) 4

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Even the idle state of the device is unpredictable Patterns exist

High variance in power consumption

Po w e r (W a tt s) Seconds (s) 5

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Changes in the OS can have profound effects

Andrew Rice, Simon Hay, Measuring mobile phone energy consumption for 802.11 wireless networking,

Pervasive and Mobile Computing, Volume 6, Issue 6, December 2010, Pages 593-606

Joules F re q u e n cy D e n si ty 6

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Android 1.1 checks that no one is using the same IP address

Time (seconds) Po w e r (W a tt s) 7

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Android 2.1 doesn’t bother checking...

Time (seconds) Po w e r (W a tt s) 8

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Consumption difference found by monitoring the network

Some effects not visible outside the device

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What’s going on inside the device?

We instrument Android’s Linux Kernel

Applications

Middleware / Services

Native interfaces

Linux Kernel

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

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Perf SystemTap FTrace KProbes DTrace Linux Trace Toolkit OProfile Valgrind

We are able to make use of existing profiling tools

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We logged every system call made during idle test using FTrace Po w e r (W a tt s) Seconds (s) 13

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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

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Example FTrace (function tracer) trace output

[Process Name] [CPU] [Time since boot]: [function] <- [parent] sh-679 [000] 131.677753: __fsnotify_parent <-vfs_write sh-679 [000] 131.677764: fsnotify <-vfs_write sh-679 [000] 131.677765: __srcu_read_lock <-fsnotify sh-679 [000] 131.677767: __srcu_read_unlock <-fsnotify sh-679 [000] 131.677772: sys_dup2 <-ret_fast_syscall sh-679 [000] 131.677773: sys_dup3 <-sys_dup2 sh-679 [000] 131.677774: expand_files <-sys_dup3 sh-679 [000] 131.677775: filp_close <-sys_dup3 sh-679 [000] 131.677776: locks_remove_posix <-filp_close sh-679 [000] 131.677778: fput <-filp_close sh-679 [000] 131.677779: __fsnotify_parent <-fput sh-679 [000] 131.677780: fsnotify <-fput sh-679 [000] 131.677781: locks_remove_flock <-fput sh-679 [000] 131.677783: module_put <-fput sh-679 [000] 131.677784: put_pid <-fput sh-679 [000] 131.677785: file_sb_list_del <-fput sh-679 [000] 131.677787: files_lglock_local_unlock_cpu <-file_sb_list_del sh-679 [000] 131.677789: drop_file_write_access <-fput sh-679 [000] 131.677790: mnt_drop_write <-drop_file_write_access sh-679 [000] 131.677791: call_rcu <-fput 15

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Annotated the first 1ms of the idle trace Po w e r (W a tt s) Seconds (s) 1ms 16

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Too much noise in the data

Power sampled at 10kHz

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Instrument individual functions with SystemTap

Applications

Middleware / Services

Native interfaces

Linux Kernel _FTrace

ST ST

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SystemTap instruments the Kernel without the need to recompile

Report back the internal state of functions Safer interface to kprobes, no more panics

Tap Script Translate to C

Build Kernel Module

Insert and run

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WiFi + TCP energy consumption appears to follow a trend 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 10 20 30 40 50 60 E ne rg y c on su m ed p er k il ob yt e ( J) Message size (kB)

Message Size (kB) En e rg y co n su me d p e r ki lo b yt e (J) 20

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We’re using SystemTap to investigate these outliers

En e rg y co n su me d p e r ki lo b yt e (J) Message Size (kB)

What’s going on inside TCP?

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We are using SystemTap to instrument the Linux TCP implementation probe kernel.function("*@net/ipv4/tcp.c").call{ printf("tcp %ul %s>%s \n",gettimeofday_s(),thread_indent(1) ,probefunc()) } 22

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

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

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