Quickboot on i.MX6
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The document discusses techniques for optimizing boot time on i.MX6 systems. It begins with an overview of the typical boot process and available measurement tools. Generic optimization techniques are then presented, such as reducing system size, stripping unnecessary features, and choosing faster storage. Specific optimizations for the bootloader, kernel, and root file system are also covered. The presentation concludes with demonstrations of solutions that achieved boot times under 1 second for critical applications on i.MX6 hardware.
Quickboot on i.MX6
- 1. Quickboot on i.MX6 FTF2014 04/10/2014 Gary Bisson Embedded Software Engineer
- 2. SESSION OVERVIEW 1. Introduction 2. Boot Process 3. Optimizations 4. Solutions 5. Demonstrations 6. Conclusion
- 3. ABOUT THE PRESENTER • Embedded Software Engineer at Adeneo Embedded (Bellevue, WA) Linux / Android ♦ BSP Adaptation ♦ Driver Development ♦ System Integration Partners with Freescale
- 4. Introduction
- 5. Quickboot on i.MX6 Introduction ARE WE TALKING ABOUT FASTBOOT? This presentation is about quick boot • Fastboot is the protocol used by Android to communicate with the bootloader in order to reflash a system on the device • Type fastboot into google: 90% hits within first 10 pages are about android Warning Fastboot is not the subject here! 5
- 6. Quickboot on i.MX6 Introduction SPEED DOES MATTER • Critical systems Automotive: need to handle CAN message within a specific time frame after boot (typically x100ms) Monitoring: need to reboot ASAP in case of failure 6
- 7. Quickboot on i.MX6 Introduction SPEED DOES MATTER Consumer are used to previous generation of non-smart devices that starts immediately • Consumer products TV: turn on quickly whenever pressing on the power button Phones: deep sleep mode allowing to have a aggressive power management policy while keeping responsiveness 7
- 8. Quickboot on i.MX6 Introduction SPEED DOES MATTER It is still possible to cheat • Display splash screen early in the bootloader (x100ms) • Animate the splash screen while booting Those tricks give the end user the illusion of a quick boot, but this could not apply to critical systems. 8
- 9. Quickboot on i.MX6 Introduction SET YOUR GOALS • Need to have clear goals: Prioritize features Set constraints • Boot-Time optimization = trade-offs 9
- 10. Quickboot on i.MX6 Introduction GOAL OF THE PRESENTATION This presentation aims at: • Showing different existing technics to optimize boot time • Explaining how to integrate those technics • Showing real customer solutions 10
- 11. Boot Process
- 12. Quickboot on i.MX6 Boot Process BOOT PROCESS 12
- 13. Quickboot on i.MX6 Boot Process BOOT PROCESS Typical i.MX6 boot process: • Boot ROM • U-Boot • Linux Kernel • Rootfs: Linux Android 13
- 14. Quickboot on i.MX6 Boot Process BOOT ROM • Boot devices: NOR Flash NAND Flash OneNAND Flash SD/MMC SATA HDD (only i.MX 6Dual/6Quad) Serial (I2C/SPI) NOR Flash and EEPROM 14
- 15. Quickboot on i.MX6 Boot Process BOOT ROM • IVT Header Entry point (fixed offset) Points to DCD table • DCD Table List of init commands • Boot data A table indicating the program image offset and size 15
- 16. Quickboot on i.MX6 Boot Process MEASUREMENT TOOLS • Grabserial Serial output time-stamps • Bootgraph Kernel driver graph • Bootchart Init scripts graph 16
- 17. Optimizations
- 18. Quickboot on i.MX6 Optimizations METHODOLOGY 18
- 19. Quickboot on i.MX6 Optimizations INTUITION The first things that comes in mind are usually: • Smaller size Loads faster (bandwidth of the storage mdevice) Loads from faster storage (NOR, MMC class 10) • Remove uneeded features Smaller system (see above) Not wasting time 19
- 20. Quickboot on i.MX6 Optimizations GENERIC OPTIMIZATIONS • lpj If your products are similar, you can set lpj Gain about 250 ms by skipping the calibration loop • Stripping init Start your critical application as soon as possible: rcS or inittab An idea may be to try to use your critical application as init 20
- 21. Quickboot on i.MX6 Optimizations GENERIC OPTIMIZATIONS • flash storage: NAND, NOR, SD We usually get really good performance booting from SD cards, class 4 or class 6, but you will still have to benchmark • toolchains Not all toolchains are created equal. Changing toolchains, will usually make you gain the last hundred of ms 21
- 22. Quickboot on i.MX6 Optimizations BOOTLOADER • U-Boot is slow? Get rid of it! • arm-kernel-shim solutions • Freescale platforms: configure just a few register then passing atags Thanks to BootROM / DCD table 22
- 23. Quickboot on i.MX6 Optimizations BOOTLOADER • Kernel may not initialize every device relies on the bootloader • Should we migrate everything to the kernel? 23
- 24. Quickboot on i.MX6 Optimizations GENERIC SOLUTIONS U-Boot Secondary Program Loader (SPL) • Small binary that fits in SRAM and loads the main U-Boot into RAM • Within U-Boot source tree, sharing same code base • Two scenarios: Fast path: SPL loads and then starts Linux kernel Development or maintenance mode: SPL loads U-Boot 24
- 25. Quickboot on i.MX6 Optimizations KERNEL OPTIMIZATIONS • Remove as many features as possible The smaller, the faster to copy from storage to RAM Less features means less initializations • Not always what you want What about a full-featured kernel? • Easy optimizations: printk and DEBUGFS try CONFIG_CC_OPTIMIZE_FOR_SIZE=y SLOB memory allocator KALLSYMS 25
- 26. Quickboot on i.MX6 Optimizations KERNEL OPTIMIZATIONS • Stripping a lot of features from is not always possible • Use modules! Load them when your critical application is ready Not always possible to compile as module (example: networking) • Kernel compression None Gzip LZO 26
- 27. Quickboot on i.MX6 Optimizations KERNEL OPTIMIZATIONS Use of deferred_initcalls • Kernel stills grows • Need to patch kernel see http://elinux.org/Deferred_Initcall • Need to modify drivers deferred_module_init • Will execute some init only when asked for (user-space) cat /proc/deferred_initcalls 27
- 28. Quickboot on i.MX6 Optimizations SMP • SMP is quite slow to initialize • UP systems may be faster to boot • Hotplug the other cores afterwards /sys/devices/system/cpu/cpuX/online 28
- 29. Quickboot on i.MX6 Optimizations ROOTFS • Multiple challenges when building your rootfs May not be able to optimize the customer’s application Even worse, you may not have the sources (blobs) Sometimes not possible to reduce the size of your rootfs 29
- 30. Quickboot on i.MX6 Optimizations ROOTFS • Use an initramfs, but use it right! • For critical tasks only • Use of uClibc reduces the size • Use of mklibs to further strip the libs • Then switch_root or pivot_root to the final rootfs 30
- 31. Solutions
- 32. Quickboot on i.MX6 Solutions SOLUTIONS • Boot from SDcard • Custom bootloader • Stripped down kernel • Start a custom init: launches critical application (CAN daemon) calls deferred_initcalls switch_root to the final rootfs and exec the final init 32
- 33. Quickboot on i.MX6 Solutions SOLUTIONS • Boot from SDcard • Custom bootloader • Stripped down kernel • Start a custom init that launches the OpenGL application • Rootfs has been stripped using mklibs • Final image (bootloader + kernel + rootfs): 5.2MB 3MB for HW blobs libraries No compression 33
- 34. Quickboot on i.MX6 Solutions RESULTS • CAN messages ready for transfer in about 360ms • OpenGL application is started in 720ms from power on 590ms from reset 34
- 35. Quickboot on i.MX6 Solutions NEXT STEPS • Use of DMA to load the image • Parallel inits • Provide a more generic solution 35
- 36. Demonstrations
- 37. Quickboot on i.MX6 Demonstrations HARDWARE SELECTION • i.MX6Q Sabre Smart Device • Kernel 3.0.35 release v4.1.0 • 10" LVDS display 37
- 38. Quickboot on i.MX6 Demonstrations SOURCE CODE • Code for the custom bootloader: https://github.com/alexandrebelloni/whoosh • Code for U-Boot SPL: coming soon... • Main inspiration was http://www.elinux.org/Boot_Time but it needs some updates 38
- 39. Conclusion
- 40. Quickboot on i.MX6 Conclusion CONCLUSION • No one-size-fits-all solution • Highly depends on constraints • Generic solution progress 40
- 41. Quickboot on i.MX6 Conclusion QUESTIONS? 41
- 42. Quickboot on i.MX6 Conclusion REFERENCES • elinux.org: http://www.elinux.org/ • Free Electrons' training: http://www.free-electrons.com/ 42