in in Mo Mobi bile le De Devices ices FAST 2015 Daeho Jeong - - PowerPoint PPT Presentation

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in in Mo Mobi bile le De Devices ices FAST 2015 Daeho Jeong - - PowerPoint PPT Presentation

Oct 20, 2023 371 likes •832 views

Boost Bo sting ing Qu Quasi si-Asynchr Asynchronous onous I/O /O for Bet Better er Res espo ponsiv nsiveness eness in in Mo Mobi bile le De Devices ices FAST 2015 Daeho Jeong *+ , Youngjae Lee + , Jin-Soo Kim * Samsung Co.,

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FAST 2015

Daeho Jeong *+ , Youngjae Lee + , Jin-Soo Kim

* Samsung Co., Suwon, Korea + Sungkyunkwan University

Bo Boost sting ing Qu Quasi si-Asynchr Asynchronous

  • nous I/O

/O for Bet Better er Res espo ponsiv nsiveness eness in in Mo Mobi bile le De Devices ices

1

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Outline

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 Introduction  Problem and Motivation  Linux Kernel I/O Path  Quasi-Asynchronous I/O  Boosting QASIOs  Evaluation  Conclusion

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Introduction

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Problem and Motivation

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 Launching the contacts APP

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Problem and Motivation

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 Burst Mode in the cameraAPP

 30 shots by touching and holding on the shot icon  When the image size is large, performance is degraded by 19%

 Installing the angry birds APP

 4GB file is written in the background  Average installation time increases by 35%

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Problem and Motivation

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 During installing or launching an app

 Many synchronous I/Os, such as read()’s or write()’s followed

by fsync() are issued

 Priority

 synchronous I/Os > asynchronous I/Os

 The progress of a file system operation is blocked by

undispatched asynchronous I/Os

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Linux Kernel I/O Path

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Ext4 orderd

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Quasi-Asynchronous I/O

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 Synchronous I/O

 The calling task is blocked until the I/O request is completed

 Asynchronous I/O  Quasi-Asynchronous I/O(QASIO)

 The I/O which is seemingly asynchronous but has the

synchronous property because one or more tasks are waiting for its completion

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Types of Dependencies on QASIO

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Direct Dependencies

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 D meta : When modifying a metadata page  D data : When modifying a data page  D sync : When guaranteeing data to be written back  D discard : When completing discard commands

 deallocate block

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D meta

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D meta

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D meta

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D meta

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D meta

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D sync

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D sync

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D sync

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D sync

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D sync

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D sync

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Indirect Dependencies

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 I jhandle : When unable to obtain a journal handle  I jcommit : When unable to complete fsync()

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I jhandle

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I jhandle

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I jhandle

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I jhandle

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I jhandle

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I jhandle

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How to Boost a QASIO

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 Req.(1): When a task is waiting for an asynchronous I/O’s

completion, the kernel gives information about QASIO to the I/O scheduler

 Req.(2): The I/O scheduler should prioritize them among

asynchronous I/Os based on the hint

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Implementation

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Implementation 1

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Detecting D meta

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 Before a task modifies a metadata page, it obtains an

exclusive lock to the metadata page using the lock_buffer() kernel function

lock_buffer() Asy IO

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Detecting D data and D sync

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Detecting D discard

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 Ext4_free_data_callback() function is called whenever the

block deallocation is required at the end of journal commit

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Implementation 2

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Evaluation

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 Samsung Galaxy S5

 Exynos 5422 (quad Cortex-A15 & quad Cortex-A7)  2GB DRAM  16GB eMMC storage (S.W

.: 54.5MB/s, R.W .: 10.4MB/s)

 Android platform version 4.4.2 (KitKat)  Linux kernel version 3.10.9

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Microbenchmarks

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 M1

 creat() -> write(4KB) -> fsync() -> close()  500 times

creat() and fsync() D meta QASIO

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Microbenchmarks

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 M2

 creat() -> write(1MB) -> fsync() -> close()  200 times

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Microbenchmarks

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 M3

 creat()  write(1KB) until file size reaches 300MB

write() D data QASIO

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Microbenchmarks

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 M4

 200M -> truncate(2M ) -> 0 -> write() -> 200M -> close()  500 times

truncate() D sync QASIO

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Microbenchmarks

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 M5

 creat() -> write(4KB) -> fsync() -> close()  another task truncates an existing 8GB file and writes 8GB of

data again to the file

I jcommit D discard QASIO

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Real-life Scenarios

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 Launching the contacts APP

44.8%

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Real-life Scenarios

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 Burst Mode in the camera APP

14.4%

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Real-life Scenarios

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 Installing the angry birds APP

11.5%

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Conclusions

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 Introduces a new type of I/O called Quasi-Asynchronous

I/O(QASIO)

 A novel scheme to detect QASIOs and boost them in the

Linux kernel

 Boosting QASIOs is effective in improving the responsiveness

  • f file system operations