Embedded Linux Evolution | Turing Techtalk

The Evolu*on of Embedded Linux

Patanjali Somayaji ([email protected])

Embedded Linux

TiVo

Roku

Leapster Explorer

Samsung Smart TV Robonaut 2

The Early Days •  Tradi*onally, Embedded Systems used “roll-‐your-‐own”,

“homegrown” or “in-‐house” RTOSes •  1980: Arrival of the first general purpose commercial embedded OS

–  VRTX (from Hunter and Ready) –  Used in the Hubble space telescope and soWware-‐controlled radio in

early Motorola Mobile phones) •  Mid-‐1980s: Increased adop*on of commercial RTOSes

–  VxWorks from WindRiver became the market leader –  Other solu*ons – QNX, Greenhills Integrity –  Embedded developer value add was in the App –  Time-‐to-‐market increasingly important

•  Linux v0.1 in 1991, by 1995 supported Alpha, i386, MIPS and Sparc architectures; and by 1996 had support for m68K and PPC

The Early Days •  1995: Busybox ini*al release to enable a small Linux image to fit on a

1.44 MB floppy –  Started by Bruce Perens to use as a Debian bootable install and rescue

disk •  1997: Linux Router Project – first embedded Linux project •  1999: Commercial RTOS industry was USD 1 Billion •  1999: The first year you could buy a commercial off the shelf

Embedded Linux Distribu*on – Montavista’s Red Hat Linux based “Hard Hat Linux”

•  1999: Linux based TiVo DVR announced (PPC 403, 16 MB RAM, 13 GB HDD)

•  2000: Embedded Linux Consor*um (ELC) – now transi*oned to the Linux Founda*on star*ng 2005

•  CE Linux Forum (CELF) – now CE working group of the Linux Foumda*on

Why did Embedded Linux grow ? •  “given enough eyeballs, all bugs are shallow” -‐ ESR

–  So reliability, which a concern in the beginning, faded away •  Linux supported MMUs providing memory par**oning and virtual

memory –  App crashes do not crash the system –  Became important as embedded systems grew in complexity –  MMUs became common in low-‐cost 32-‐bit embedded systems –  uCLinux developed for MMU-‐less high volume, cost-‐sensi*ve markets

•  Royalty free –  No license free per unit deployed, unlike commercial RTOSes –  Commercial linux is usually sold on a developer-‐seat license basis –  Important for large scale embedded deployment which is cost sensi*ve

•  No dependency on a single OS vendor for a cri*cal component of embedded applica*on

Why did Embedded Linux grow ? •  Networking was usually a paid-‐for extra on commercial RTOSes.

Linux was built with networking support from the ground up. •  Open source alterna*ve – Net BSD

–  NetBSD was mature, open source and gemng established at the same *me

–  Linux however was based on GPLv2 which triggered a lot of give-‐back –  More drivers and architectures started to get support, and there was a

massive Network effect •  ARM processors were heavily adopted, and Linux was ported to

various SoCs and development planorms •  Linux development in other areas e.g. Servers were leveraged in

Embedded systems e.g. Networking, CPU Hotplug

Embedded Linux -‐ Networking •  The Linux Router Project (LRP) – the

first embedded Linux project ? •  Pioneering features

–  Small base OS footprint –  A simplified packaging system –  Menu based system and package

configura*on –  Strict separa*on of vola*le, non-‐

vola*le, Read Only, and Read/Write areas of the root hierarchy

–  Unpacked and run from ramdisk or run directly from flash

–  A system to commit configura*on changes to a non-‐vola*le medium (Disk/Flash)

•  Spawned a deluge of Embedded Linux Networking Devices

Cisco Linksys WRT54GL Wireless-‐G Broadband Linux Router

“Every age had its own kind of war, its own limi*ng condi*ons, and its own peculiar preconcep*ons” – Carl von Clausewitz, German-‐Prussian Soldier & Military Strategist

Real-‐*me Linux

•  Different approaches –  TimeSys introduces proprietary Linux/RT 1.0 –  FSM Labs RTLinux (commercially licensed)

•  Real-‐*me kernel running Linux as a low-‐priority thread •  Posix API to run real-‐*me threads from User Space •  Under 15 micro-‐second response (Year 2000) •  Acquired by WindRiver in 2007

– MontaVista worked on kernel pre-‐emp*on •  Meanwhile the Linux Kernel developers were working on their solu*on

Real-‐*me Linux •  2000 – Ingo Molnar and Andrew Morton start work on voluntary

pre-‐empt “CONFIG_PREEMPT_VOLUNTARY” –  Reduce worst-‐case interrupt latencies –  Break lengthy kernel cycles into smaller chunks and add checks to

common causes of long latencies –  Rescheduling if an interrupt handler has set the “need_resched” flag –  Eventually merged in Linux Kernel 2.6

•  2001 – Robert Love began work on the kernel pre-‐emp*on “CONFIG_PREEMPT” –  Ini*ally based on MontaVista patch –  Target low-‐latency apps and smooth user interac*on –  Makes kernel pre-‐emp*ble like user-‐space, allowing higher priority

tasks to run -‐ all kernel code outside of spinlock-‐protected regions and interrupt handlers eligible for pre-‐emp*on

–  Adopted by MontaVista in MVL 4.0 and merged with Linux Kernel 2.6

Controlling a laser with Linux is crazy, but everyone in this room is crazy in his own way. So if you want to use Linux to control an industrial welding laser, I have no problem with your using PREEMPT_RT.” -‐ Linus Torvalds

Real-‐*me Linux

•  2005 – Ingo Molnar and others began work on CONFIG_PREEMPT_RT –  Convert Linux Kernel into a fully pre-‐emp*ble kernel

•  In-‐kernel locking primi*ves made pre-‐emp*ble •  Cri*cal sec*ons made pre-‐emp*ble (crea*on of non-‐pre-‐emp*ble sec*ons s*ll possible)

•  Implemented priority inheritance for in-‐kernel spinlocks and semaphores

•  Converted interrupt handlers to pre-‐emp*ble kernel threads •  Converted Linux *mer API into separate infrastructures for high resolu*on *mers and *meouts

•  10 to 30 micro-‐second scheduler and interrupt latencies

Real-‐*me Linux •  Patches for Linux 2.6 Kernel suppor*ng Real-‐*me

–  Preemp*ble Interrupt Handlers in Thread Context –  IRQ-‐Disable Virtualiza*on for Drivers

•  IRQ threads disabled without masking hardware –  Integrated Kernel Mutex with Priority Inheritance (PI)

•  Protec*on of Kernel Cri*cal Sec*ons by Preemp*ble PI Mutex –  PI Mutex Subs*tuted for Non-‐Preemp*ble Kernel (SMP) Locks

•  Big Kernel Lock (BKL) converted to PI Mutex •  Spin-‐Locks converted to PI Mutex •  Read-‐Write Locks converted to PI Mutex •  RCU Preemp*on Enhancements

–  High Resolu*on Timers –  User-‐Space Mutex

•  Robustness/Dead-‐owner/Priority Queueing

ARM is Everywhere •  Smartphones •  Inexpensive evalua*on boards –  BeagleBoards –  BeagleBones –  Raspberry Pi

•  Now also coming for Servers – AMD to release its first “Seaule” ARM Server Chip in 2014

Source: hup://arstechnica.com/business/2012/08/from-‐altair-‐to-‐ipad-‐35-‐years-‐of-‐personal-‐computer-‐market-‐share/

ARM Linux •  Started out in 1994 as a port of the 1.0.x kernel to the

Acorn 5000 •  1999 Linux 2.2.0 – ARM architecture added to mainline •  Variety of architectures, Kernel Patches and drivers

–  Hardware varies from SoC to SoC –  Development planorm divergence

•  “ARM Wrestling” –  Grew to be a massive collec*on of “subplanorms” –  Managed independently by different developers –  “ARM support is a labyrinthine maze of wheels within reinvented wheels”

•  Linaro formed in 2010 to drive common development and integra*on

“I think the more serious long-‐term issue we have in the kernel is the wild and crazy embedded planorm code (and mostly ARM -‐ not because ARM is in any way fundamentally crazier, but because ARM is clearly the most successful embedded planorm by far). The embedded world has always tended to eschew standardized planorms: they've been resource constrained etc, so they've done very tailored chip and board solu*ons, and felt that they couldn't afford a lot of planorm abstrac*on.” -‐ Linus Torvalds – May 2011

Mobile Linux …

2001/2002: Sharp Zaurus SL-‐5500 running OpenZaurus and OPIE SA-‐1110 CPU @ 206 MHz, 64 MiB RAM, 16 MiB NOR

2003: Motorola A760 ARM 925 chip (an Intel PXA270) at 316 MHz, 48 MiB flash storage, QVGA (240 x 320) touch screen

2008: HTC/T-‐Mobile G1 Qualcomm MSM7210A (ARM11) processor running @ 528 MHz, 256 MiB NAND flash storage, 192 MiB RAM, 3.2-‐inch touchscreen (320 x 480). Launched with Android 1.0 based on modified Linux 2.6.25

2005: Nokia N770 Tablet TI OMAP 1710 @ 252 MHz 64 MB RAM, 128 MB Flash 4.1 inch touchscreen (800 x 480). Launched on Maemo/Linux

… and Mobile Linux Consor*ums

Brief Interlude: Embedded Filesystems •  Ini*al configura*ons

–  Expensive NOR Flash for Cri*cal storage –  Cheaper and denser NAND Flash for larger capaci*es –  NAND flash used in consumer devices

•  Flash usage needed “wear-‐leveling” to spread the block erases evenly •  Ini*al Linux support for read-‐only FS (no need for wear-‐levelling)

–  CramFS & SquishFS •  Since Flash connected as raw memory devices, Linux needed to handle intelligently

for RW via the Linux MTD Interface (Memory Technology Device) –  JFFS2, YAFFS2, LogFS, UBIFS

•  Smartphones evolved to using eMMC –  Large volume of NAND storage with a controller –  Connect as block devices –  Use flash vendor’s flash wear-‐leveling algorithms

•  2012: F2FS –  SoWware layer to handle “smartness” outside the Flash Transla*on Layer (FTL) –  Targeted at SSDs, eMMC, SD Cards and other Flash storage with FTL –  Flash wear-‐leveling in controller

Brief Interlude: Power Management

•  Embedded Linux – started off with Routers, etc. “plugged in” devices so Power Management was not a priority

•  PM focused mostly on Desktop/Laptop/Server support –  APM (1992 Intel & MicrosoW)

•  PM in BIOS, BIOS HW specific •  Reduce CPU, turn-‐off Display, disable Harddisk aWer *me-‐out

–  ACPI (1996 v1.0 open standard industry specifica*on) •  OS controls PM, BIOS provides API

•  Power Management cri*cal for Mobile Phones – supported on ARM SoCs with the usual fragmenta*on

•  Integra*ng Power Management in drivers and kernel is a major ac*vity for the Mobile OEM

Brief Interlude: Power Management •  Power Management mechanics

–  System Suspend – User forces system to sleep –  CPU idle – Idle thread triggers sleep states –  CPU freq – CPU frequency scaling –  Run*me PM – Device Power Management –  CPU Hotplug – Remove a CPU from the running system (ini*ally used for

Server SMP Linux became important for mul*-‐core ARM) •  Due to a lack of a standard like ACPI, ARM SoCs support is fragmented

–  ARM SoCs expose a lot of HW knobs to SoWware, directly controlled by the OS drivers

–  Each SoC vendor exposes a superset of standard ARM power states for fine-‐grained control, increasing complexity of SoC enablement code and peripheral drivers

–  Different approaches to OS Power Management frameworks due to a lack of design pauerns, lack of common infrastructure and intrinsic HW differences

–  Linaro approach to integrate and unify

hups://wiki.linaro.org/WorkingGroups/PowerManagement/Doc/Architecture

Android “wakelock”

•  Default state is to suspend •  Kernel implementa*on and Android user-‐space APIs – When a wakelock of type “WAKE_LOCK_IDLE” is in effect, system does not enter Idle (low power)

– When a wakelock of type “WAKE_LOCK_SUSPEND” is in effect, system will not suspend

•  Highly controversial feature, mul*ple patch submissions and mailing list discussions over many years

•  Compa*ble solu*on being mainlined in later Kernel 3.x series

Is Android the new “Embedded Linux” ?

Android

“The interes*ng thing about Android’s design is how liule we modified the kernel. Most embedded systems on which I have worked have made dras*c changes to the kernel, only to leave user-‐space alone — for example, a heavily-‐modified “real*me” kernel but X11 for a GUI. Android is the opposite: Only minimal changes to the kernel, but a user-‐space wholly unlike that of any other Unix system. In fact, Android’s user-‐space is so different from stock Linux, you can easily say that Android is not in any way a Linux system, except for the kernel.” -‐ Robert Love, Google Engineer and Kernel Contributor

hup://www.forbes.com/sites/quora/2013/05/13/what-‐are-‐the-‐major-‐changes-‐that-‐android-‐made-‐to-‐the-‐linux-‐kernel/

Android •  ashmem (Android Shared Memory), a file-‐based shared memory system •  Binder, an inter-‐process communica*on (IPC) and remote procedure call

(RPC) system •  logger, a high-‐speed in-‐kernel logging mechanism op*mized for writes •  Paranoid Networking, a mechanism to restrict network I/O to certain

processes •  pmem (Physical Memory), a driver for mapping large chunks of physical

memory into user-‐space •  Viking Killer, a replacement OOM killer that implements Android’s “kill

least recently used process” logic under low memory condi*ons •  wakelocks, Android’s unique power management solu*on, in which the

default state of the device is sleep and explicit ac*on is required (via a wakelock) to prevent that

•  The usual assortment of drivers, ARM architecture ports, and other associated low-‐level code necessary to support Android on any given device

hup://www.forbes.com/sites/quora/2013/05/13/what-‐are-‐the-‐major-‐changes-‐that-‐android-‐made-‐to-‐the-‐linux-‐kernel/

Android

•  Android is the most popular Embedded Linux “distro” today

•  From hos*lity to gradual adop*on – E.g. mainlining of selec*ve Android features in Linux Kernel

– Ubuntu “MIR” display server across Desktop/Tablet/Phones leverages Android display drivers and architecture

– We all love “adb”

Looking ahead …

Linaro •  Not-‐for-‐profit engineering

organiza*on consolida*ng and op*mizing open source Linux soWware and tools for the ARM architecture

•  Focus on generic ARM technology common to all ARM SoC vendors

•  Focus on areas that interact directly with silicon like Mul*media, Graphics, Power Management, Kernel and Boot

•  Maintenance, up-‐streaming and implementa*on of standards

•  Established in 2010 by ARM, Freescale, IBM, Samsung, ST-‐Ericsson and Texas Instruments

Yocto Project

•  Not an embedded Linux distribu*on – Yocto provides tools to build a custom embedded Linux distribu*on

•  Based on Poky, OpenEmbedded •  Provides Linux Kernel, System Libraries, UI Framework

•  Op*onal Sato user interface based on GNOME Mobile Stack

Yocto Project

Genivi •  Industry non-‐profit alliance to drive adop*on of open source In-‐vehicle Infotainment development planorm

•  Launched in Mar 2009 •  Linux-‐based kernel, core services, middleware and open applica*on interfaces

•  Genivi compliant – Tizen, MontaVista IVI, Ubuntu Remix IVI, WindRiver IVI

Tizen •  History – builds on SLP from LiMo, formed when Intel leW Meego to join Tizen

•  Open-‐source, standards based planorm for Smartphones, Tablets, In-‐vehicle Infotainment Devices, Smart TVs

•  Part of the Linux Founda*on •  Devices from Samsung “later in 2013”

Ubuntu for Smartphones

•  Built on Ubuntu Linux, leverages Android Tech

•  HTML5 and Na*ve Apps are equal ci*zens

•  Same OS across devices, same OS across same device in different form factors

•  OEM Customizable •  Phones in 4Q2013/early 2014

If you’re confused …

Source: hups://github.com/kumadasu/*zen-‐history/blob/master/*zen-‐history.pdf

Not to forget …

Firefox Mobile

•  “Boot to Gecko” -‐> Linux + Mozilla Gecko

•  Web as the Applica*on Planorm

•  Leverages HTML5 and other Web Standards

•  Devices launching “soon”

Sources Google and Wolfram Alpha hup://www.embedded-‐linux.co.uk/embedded-‐history hup://www.arm.linux.org.uk/docs/history.php hup://lwn.net/Ar*cles/437162/ hup://www.linuxjournal.com/ar*cle/5755 hup://en.wikipedia.org/wiki/Carl_von_Clausewitz hups://rt.wiki.kernel.org/index.php/Main_Page hup://elinux.org/images/b/ba/Elc2013_Rostedt.pdf hups://lwn.net/Ar*cles/518988/ hup://en.wikipedia.org/wiki/Sharp_Zaurus hup://en.wikipedia.org/wiki/Nokia_770_Internet_Tablet hups://wiki.linaro.org/WorkingGroups/PowerManagement hups://www.kernel.org/doc/Documenta*on/cpu-‐hotplug.txt hup://elinux.org/Power_Management hup://www.itworld.com/mobile-‐wireless/175829/arm-‐and-‐linux-‐major-‐construc*on-‐ahead hup://arstechnica.com/business/2012/08/from-‐altair-‐to-‐ipad-‐35-‐years-‐of-‐personal-‐computer-‐market-‐share/ hup://www.pcworld.com/ar*cle/2042267/amd-‐slates-‐first-‐arm-‐server-‐chip-‐seaule-‐for-‐2014.html hup://www.slideshare.net/opersys/is-‐android-‐the-‐new-‐embedded-‐embedded-‐linux-‐at-‐embedded-‐wordl-‐2013

hups://wiki.linaro.org/WorkingGroups/PowerManagement/Doc/Architecture hup://www.forbes.com/sites/quora/2013/05/13/what-‐are-‐the-‐major-‐changes-‐that-‐android-‐made-‐to-‐the-‐linux-‐kernel/ hup://training.linuxfounda*on.org/free-‐linux-‐training/download-‐training-‐materials/history-‐of-‐embedded-‐linux-‐and-‐best-‐prac*ces-‐for-‐gemng-‐started hup://en.wikipedia.org/wiki/Linux_Router_Project hup://www.extremetech.com/extreme/155392-‐interna*onal-‐space-‐sta*on-‐switches-‐from-‐windows-‐to-‐linux-‐for-‐improved-‐reliability hup://www.linaro.org hup://yoctoproject.org hup://*zen.org hup://www.ubuntu.com/phone hups://github.com/kumadasu/*zen-‐history/blob/master/*zen-‐history.pdf hup://www.mozilla.org/en-‐US/firefox/os/

Embedded Linux Evolution | Turing Techtalk

Technology

Transcript of Embedded Linux Evolution | Turing Techtalk