Status of Embedded Linux

Status of Embedded Linux

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  ConfidentialPA110/23/20141 Status of Embedded Linux Statusof Embedded Linux June 2017 Tim Bird Architecture Group Chair LF Core Embedded Linux Project 1
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  ConfidentialPA110/23/20142 Nature of thistalk… • Quick overview of lots of embedded topics • A springboard for further research • If you see something interesting, you have a link or something to search for 2
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  ConfidentialPA110/23/20143 Outline Kernel Versions Technology Areas CEWorkgroup Projects Other Stuff Resources 3
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  ConfidentialPA110/23/20144 Outline Kernel Versions Technology Areas CEWorkgroup Projects Other Stuff Resources 4
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  ConfidentialPA110/23/20145 Kernel Versions • Linuxv4.7 – 24 July 2016 – 70 days • Linux v4.8 – 2 Oct 2016 – 70 days • Linux v4.9 – 11 Dec 2016 – 70 days • Linux v4.10 – 19 Feb 2017 – 70 days • Linux v4.11 – 30 Apr 2017 – 70 days • Linux v4.12-rc5 - • v4.12 expected on 9 July, 2017 5
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  ConfidentialPA110/23/20146 Linux 4.7 • Schedutilfrequency governor • Use the load calculated by the scheduler instead of the average load over past little while • See http://lwn.net/Articles/682391/ • VFS layer can iterate through directories in parallel • Ability to attach BPF programs to tracepoints • Ftrace histogram triggers • Can tell tracer to accumulate events into buckets and give results, via the sysfs interface • Android sync_file feature moved from staging • Support for explicit buffer fencing 6
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  ConfidentialPA110/23/20147 Linux 4.8 • Newkernel documentation system • New pseudo-random number generator • See https://lwn.net/Articles/686033/ • ARM64 support for kexec and kprobes • New timer wheel implementation • https://lwn.net/Articles/646950/ • Better performance: • No more cascade operations • Quick determination of next timout • Automatically coalesces longer timeouts • Long timeouts have reduced resolution 7
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  ConfidentialPA110/23/20148 Linux 4.9 • Virtuallymapped kernel stacks • http://lwn.net/Articles/692953/ • Allows to detect stack overruns • Cleans up kernel code, faster process creation • Only on x86, for now • Greybus - https://lwn.net/Articles/715955/ • Timed samples for eBPF • Modversions deprecated • See https://lwn.net/Articles/707520/ 8
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  ConfidentialPA110/23/20149 Linux 4.10 • Perfsched timehist • Hybrid block polling • Supports polling for block I/O, but with a short delay (estimated) before the polling starts • Improves performance by queuing blocks as soon as device is ready (via polling) • Uses less CPU than full polling • Support for ARM SoCs: • Huawei, Allwinner, Marvel, Renesas • Posix timers are configurable • Initramfs compression method is selectable • New interface for system sleep state selection • /sys/power/mem_sleep • UBIFS support for encryption 9
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  ConfidentialPA110/23/201410 Linux 4.11 • Newkernel refcount API • TinyDRM subsystem added • New statx() system call • https://lwn.net/Articles/707602/ • 2038-safe time values • Mask of fields to obtain (for efficiency) • Sched.h refactoring • Non-mainline code: watch out! 10
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  ConfidentialPA110/23/201411 Linux 4.12 (expected) •BFQ and Kyber block I/O schedulers • Minitty prep work • Not full minitty implementation yet • Proper support for USB type-C connectors • AnalyzeBoot tool • Reads dmesg (and possibly ftrace log) and produces html graph of boot events • Part of Intel pm-graph tools project • https://github.com/01org/pm-graph • See tools/power/pm-graph/analyze_boot.py 11
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  ConfidentialPA110/23/201412 Outline Kernel Versions Technology Areas CEWorkgroup Projects Other Stuff Resources 12
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  ConfidentialPA110/23/201413 Bootup Time • Nonew work in kernel, that I’m aware of • Analyze_boot tool – new in in 4.12 • Some good previous talks: • ELCE 2014 - 12 Lessons Learnt in Boot Time Reduction by Andrew Murray • ELC 2015 - Fastboot Tools and Techniques by John Mehaffey • Android boot time ideas • ELC 2017 – Improving the bootup speed of AOSP – Bernhard Rosenkranzer 13
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  ConfidentialPA110/23/201414 Bootup ideas fromBernhard • Two approaches: • Improve cold boot • Enhance suspend/resume • Areas analyzed for cold boot: • Package Manager scanning • Java class preloading • PM: force high CPU frequency during boot • IO: read-ahead, kernel compression, squashfs • Kernel modules – defer modules until later • Library and compiler optimizations
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  ConfidentialPA110/23/201415 Device Tree • DeviceTree Overlays • Allow plugin-boards to be configured at runtime • Session at ELC 2016 by Pantellis • Not mainlined yet? – expected in 4.11? • Device Tree validation • Schema for binding language, validator for bindings and for device tree data • This work stalled • Updated Device Tree specification • Being discussed • Want to update material and make it more available • See http://elinux.org/Device_tree_plumbers_2016_etherpad • And ELC 2017 Device Tree BOF – Frank Rowand 15
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  ConfidentialPA110/23/201416 Graphics • TinyDRM • Providesgraphic support for small simple displays (eg displays over i2C or SPI) • Hope to replace framebuffer drivers over time • See https://www.phoronix.com/scan.php?page=news _item&px=TinyDRM-Patches-Posted • GPU support: • ARM mali drivers status update • https://lwn.net/Articles/716600/ • Presentation • ELC 2017 What Can Vulkan do for You? - by Jason Ekstrand 16
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  ConfidentialPA110/23/201417 File Systems • UBIFSsupport for encryption (in 4.11) • IO scheduling for solid state storage • LightNVM • Software control of flash-translation layer • https://lwn.net/Articles/641247 17
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  ConfidentialPA110/23/201418 Networking • Bluetooth: • Bluetooth5.0 • Most features are on BLE codebase • Only 1 for “BL classic” • 800% data throughput increase • 4 times the range • Coexistence with wireless • Better error correction to handle noisy environments 18
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  ConfidentialPA110/23/201419 Power Management • Newinterface for system sleep state selection (in 4.10) • /sys/power/mem_sleep • Operating-System-Directed Power- Management Summit • https://lwn.net/Articles/721573/ • Energy-aware scheduling • A collection of scheduling talks that will make your head spin
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  ConfidentialPA110/23/201420 Real Time • SCHED_DEADLINE •ELC 2017 - SCHED_DEADLINE: It’s Alive - by Juri Lelli • Energy Aware Scheduler support • Bandwidth reclaiming • Temporarily allow a task to exceed it’s bandwidth, if no other process’ deadline suffers • Support for Frequency scaling • Group scheduling • Presentations: • ELC 2017 Effectively Measure and Reduce Kernel Latencies for Real-time Constraints – By Jim Huang • ELC 2017 Real-Time Linux on Embedded Multicore Processors – by Andres Ehmanns 20
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  ConfidentialPA110/23/201421 Security • Kernel hardening •http://kernsec.org/wiki/index.php/Kernel_Self_Protection_ Project • Rare_write infrastructure • Keep some code and data read-only most of the time • https://lwn.net/Articles/724319/ • GCC plugins for kernel security • Kernexec • Prevent kernel from executing user-space code • Structleak (mainlined in 4.11) • Zero out kernel structures passed to user space, under some conditions • See https://lwn.net/Articles/712161/ • Randstruct • Randomize C structure layout • See https://lwn.net/Articles/722293/ 21
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  ConfidentialPA110/23/201422 Security Presentations • ELC2017 Securing Embedded Linux Systems with TPM 2.0 – by Philip Tricca
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  ConfidentialPA110/23/201423 System Size • Initramfscompression method is selectable • Nicolas Pitre work • Configurable POSIX timers – in v4.10 • https://lwn.net/Articles/701095/ • Mini TTY • Smaller implementation of TTY subsystem, for embedded • Saves about 38K • https://lwn.net/Articles/721074/ • People wanted refactoring of full-size TTY instead of new small implementation, but Nicolas said that wasn’t feasible 23
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  ConfidentialPA110/23/201424 System Size (cont.) •Shrinking the scheduler • Drops features and eliminates realtime and deadline scheduler classes • Saves about 20k • https://lwn.net/Articles/725376/ • Lots of resistance to this • Code complexity increase is not worth saving 20k (according to Ingo Molnar) • Disagreement on whether Linux should support computers with sub-1MB memory
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  ConfidentialPA110/23/201425 Size Presentations • LinuxConNorth America: Running Linux on Tiny Peripherals – by Marcel Holtmann • Got Linux to around 1MB for IOT sensor project • ELC 2017 Embedded Linux Size Reduction Techniques – By Michael Opdenacker • Very good overview of existing reduction techniques and status • Formal Tinification project is stalled • Toybox and musl (smaller libc) are worth looking at
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  ConfidentialPA110/23/201426 Testing • Kselftest • Fuego •Kernelci.org • LAVA V2 26
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  ConfidentialPA110/23/201427 Kselftest • Unit testsystem inside kernel source tree • Recent work: • Lots more regression tests (preferred place for syscall compatibility/regression tests (over LTP) • Converting to TAP (Test Anything Protocol) for test output
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  ConfidentialPA110/23/201428 Fuego • New TestFramework for collaborating on tests and test infrastructure for Linux • V1.1 features (April 2017) • Upgrade to latest Jenkins • Test script refactoring • Fuego container directory layout change • About 40 new tests • V1.2 plans (RC in July) • Unified output format • Convert all test results to JSON • Support LAVA as a transport & board manager • Test dependency system • Board dynamic variables
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  ConfidentialPA110/23/201429 Kernelci.org • Place toget free build/boot testing for your board • Builds 126 trees continuously, then reports any errors • http://kernelci.org • Presentations: • ELC and ELCE 2016 – by Kevin Hilman • Linaro Connect: • Kernelci and lava update - See https://lwn.net/Articles/716600/ • The most successful public, distributed build and test system for Linux, in the world! 29
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  ConfidentialPA110/23/201430 LAVA • Linaro Automationand Validation Architecture • V2 • Job files now use Jinja2 templates • Was previously hand-written JSON • Jobs are run asynchronously, without polling, • ZeroMQ is used for communications. • ReactOBus is used to run jobs from messages. • Requires more explicit board configuration
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  ConfidentialPA110/23/201431 Toolchains • LLVM 4.0.0is released • Some code size improvements from optimizations (GVNHoist) • Experimental support for LLVM coroutines • https://lwn.net/Articles/716979/ • Presentations: • ELC 2017 - GCC/Clang Optimizations for Embedded Linux – by Khem Raj 31
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  ConfidentialPA110/23/201432 Tracing • More perftools (both in 4.10): • perf sched timehist • Analysis of scheduling events • perf c2c • Cacheline contention analysis • Presentations: • ELC 2017 Dynamic Tracing Tools on ARM/AArch64 Platform: Updates and Challenges - by Hiroyuki Ishii • Great overview 32
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  ConfidentialPA110/23/201433 Miscellaneous • Year 2038status: • 3 areas of work: • Converting all 32-bit timestamps to 64-bit in the kernel • e.g. New statx() system call • Many patches are in-progress (vfs layer, v4l, device- mapper, input subsystem) • C libraries • Lots of work in glibc to make everything backwards compatible • Even programs built with 32-bit timestamps should work • Distribution builds • See https://lwn.net/Articles/717076/ 33
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  ConfidentialPA110/23/201434 Outline Kernel Versions Technology Areas CEWorkgroup Projects Other Stuff Resources 34
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  ConfidentialPA110/23/201435 Projects and initiatives •Shared Embedded Distribution • LTSI • Fuego • eLinux wiki 35
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  ConfidentialPA110/23/201436 Shared Embedded Distribution •Goals • Create an industry-supported distribution of embedded Linux • Main goal is very long term support (15 years) • Status • Toshiba has created Yocto layer meta-Debian • Presented at ELCE, ELC, and LCJ • Next steps • Improve coordination with Debian community 36
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  ConfidentialPA110/23/201437 Long Term SupportInitiative • LTSI 4.9 is current LTSI kernel • Work is in progress on next release • GregKH said • Expected delivery date: Sep 2017 • Converting to upstream-first policy • Presentation: • ELC 2017 Using Linux as Long Term Working with the Community – by Tsugikazu Shibata 37
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  ConfidentialPA110/23/201438 Fuego - LinuxTest Framework • Working on lots of issues: • Command line tool • Test packaging • LAVA integration • Serial console transport • Presentation: • ELC 2017 BoF: Fuego Status and Roadmap – by Tim Bird 38
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  ConfidentialPA110/23/201439 eLinux wiki • http://elinux.org •Web site dedicated to information for embedded Linux developers • The wikipedia of embedded linux! • Hundreds of pages covering numerous topic areas: bootup time, realtime, security, power management, flash filesystem, toolchain, editors • Lots of pages in last few years about low- cost development boards • Please use and add to site 39
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  ConfidentialPA110/23/201440 Outline Kernel Versions Technology Areas CEWorkgroup Projects Other Stuff Resources 40
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  ConfidentialPA110/23/201441 Trade Associations • Linarostill doing lots of great work • Lava v2 and kernelci • Now promoting Zephyr • Linaro Connect consistently has useful material • Linux Foundation • Microsoft has joined the Linux Foundation as a platinum member • CE Workgroup officially changed its name to “Core Embedded Linux Project”
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  ConfidentialPA110/23/201442 Conferences • ELC 2017 •Lots of great sessions • See: http://elinux.org/ELC_2017_Presentations • Open Source Summit Japan • May 31-June 2, Tokyo • Embedded Linux Conference Europe • October 23-25, Prague, Czech Republic • Embedded Linux Conference • March 12-14, Portland, Oregon, USA • Japan Jamborees • Continuing
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  ConfidentialPA110/23/201443 ELC 2017 thoughts •Linus and Dirk fireside chat • 4.10 release was calm • 4.9 was a bit bigger due to LTS pre-announcement • Linus thinks is healthier to not push things based on a deadline, but 4.9 wasn’t too bad • Even after all these years, we see changes to core files • Linus said that Linux is general-purpose, so may not be appropriate for the lowest-footprint device • I feel vindicated
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  ConfidentialPA110/23/201444 Outline Kernel Versions Technology Areas CEWorkgroup Projects Other Stuff Resources 44
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  ConfidentialPA110/23/201445 Resources • LWN.net • http://lwn.net/ •If you are not subscribed, please do so • Kernel Newbies • http://kernelnewbies.org/Linux_[34].? • eLinux wiki - http://elinux.org/ • Especially http://elinux.org/Events for slides • Celinux-dev mailing list 45
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  ConfidentialPA110/23/201446 Thanks! 46