Storage-aware Smartphone Energy Savings
Reducing Smartphone Application Delaythrough Read/Write Isolation
David T. Nguyen
David T. Nguyen2Figure Courtesy: Facebook Connectivity Lab
Real-world Problem: Application Delay
David T. NguyenWilliam & Mary2
IntroductionResearch questionsHow does disk I/O affect smartphone application response time?How to optimize storage to improve application performance?
ContributionsFirst large-scale Android I/O study on 2611 devicesProposed SmartIO scheduler that reduces application delayEvaluation indicates 21% reduced launch and 17% reduced run-time delay
David T. Nguyen3
www.StoreBench.comStoreBench Benchmark4
David T. Nguyen
40% devices between 13% and 58% Significant CPU time spent waiting for storage
Iowait of 2611 DevicesCPU active time spent waiting for storage I/O5David T. Nguyen
David T. NguyenWilliam & Mary5
Seq. reads experience up to 626% slowdown when blocked by concurrent writes (rand. up to 293%)I/O slowdown possible source of worse app launch (reads dominate)
I/O Slowdown6
David T. Nguyen
Slowdown Asymmetry 7
ReadSlowdown = Response time of a read in the presence of a concurrent write / Response time of a read when running aloneWriteSlowdown = Response time of a write in the presence of a concurrent read / Response time of a write when running aloneRead slowdown up to 6.15 vs. write slowdown up to 1.6
David T. Nguyen
Study SummaryAndroid devices spend up to 58% of CPU active life time idling due to I/O
Reads experience up to 626% slowdown when blocked by concurrent writes
Large slowdown asymmetry (reads up to 6.15; writes up to 1.6)8David T. Nguyen
I/O Scheduler Storage SubsystemConcurrency ProfilerI/O GroupingI/O Dispatch
I/O Priority Assignment
Kernel SpaceUser Space
SmartIODavid T. Nguyen9
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FLASH BLOCK DEVICE
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 7
queuequeue
IdleBest EffortReal-time
writereadDispatchQueue Real-timeBest EffortIdle
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Demo SmartIO11
Nexus 4: 1-reader (128MB), 1-writer (128MB)Seq. read slowdown improves from 6.15 to1.72 (gain), write worsens from 1.13 to 1.51 (cost)Rand. read slowdown improves from 3.18 to 1.97 (gain), write worsens from 1.6 to 1.83 (cost)
Gain vs. Cost12
David T. Nguyen
128MB mixed workload (first 10% reads, then 20%..)With increasing percentage of reads, response time decreases (less writes means less slowdown)By changing scheduler (default CFQ to SmartIO) we achieve on average 49% faster response (max. 66%)
Scheduler Comparison13
David T. Nguyen
Cold launch delays reduced on average by 21% (warm by 13%)Run-time delays reduced by 17%
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David T. Nguyen
Facebook Inc.s goal: cold launch < 5s on 2012 or newer devicescold launch < 10s on older devicesRAZR (2012): 9.9s -> 6.2sSamsung S5 (2014): 3.7s -> 2.3sFacebook Performance15
David T. Nguyen
Conclusion & Future WorkSmartIOReduces app delays through read/write isolation and higher read priorities
Study other stages of app life cycle (install, update, switch, uninstall)
Analyze impact of network I/O16David T. Nguyen
AcknowledgmentsOur shepherd Prof. Mahadev Satyanarayanan (CMU)Aaron Carroll (NICTA), Dr. Duy Le (EMC), Dr. Tommy Nguyen (RPI), Mai Anh Do (CNU), Daniel Graham (W&M)17
David T. Nguyen
Reducing Smartphone Application Delaythrough Read/Write Isolation
David T. Nguyen