Embedded Linux BOF Tim Bird Sony Corporation CE Linux Forum Architecture Group Chair Ottawa Linux Symposium – July 23, 2008.

Embedded Linux BOF

Tim BirdSony Corporation

CE Linux Forum Architecture Group Chair

Ottawa Linux Symposium – July 23, 2008

Outline

Big News! Kernel Version Highlights Technology Watch List Other news Status Resources Discussion

BIG Community News!!

linux-embedded mailing list has been created!! There are now “Embedded Linux” maintainers!! Based on Andrew Morton talk at Embedded

Linux Conference, and succeeding discussion Also, Andrew worked behind-the-scenes to help

make these things happen

linux-embedded mailing list

Is now the main list for kernel-related embedded patches and discussion Lower traffic than LKML – should be much easier to watch

Technical discussions about the kernel should be moved here from linux-tiny, celinux-dev, and others

How to subscribe and access archives: http://vger.kernel.org/vger-lists.html#linux-embedded

You should subscribe!

New embedded Linux maintainers

Who: David Woodhouse – MTD/JFFS2/OLPC guy Paul Gortmaker – longtime kernel developer

What: Keep track of patches and technology

development related to embedded Handle stuff that has no other home See LWN.net interview of maintainers at:

http://lwn.net/Articles/284767/

Kernel Highlights

Previous kernel highlights 2.6.26 highlights Coming in 2.6.27 Interesting patches (Tim’s list)

2.6.24 Kernel Highlights

Kernel markers Loadable Security Modules framework was

removed PM Quality of Service (QOS)

Markers

Infrastructure in kernel for static instrumentation Kprobes are for dynamic instrumentation Used by SystemTap and Linux Trace Toolkit(ng)

Goal is very low overhead when not in use One compare, using immediate value

No memory access or cache/TLB usage issues There's a new system to replace immediate values in

kernel code, while the kernel is running!!

New “tracepoint” feature (see Matthieu Desnoyer’s presentation – Friday 10:00)

2.6.25 Kernel Highlights

Kpagemap Matt Mackall's patches for fine-grained memory

instrumentation (more on next slide) Latency measurement API

Support for LatencyTop See http://lwn.net/Articles/266153

SMACK - simple mandatory access control New lightweight MAC system for kernel, by Casey

Schaufler Go to OLS Session Saturday at 10:00 for more info

(“SMACK in embedded computing”)

Kpagemap

Can show details about every allocated (and virtual) page on the system

Introduces PSS and USS size metrics PSS = Proportional Set Size USS = Unique Set Size

Resources: ELC presentation

http://selenic.com/repo/pagemap/raw-file/tip/memory-profiling.html

LWN.net article: http://lwn.net/Articles/230975/

Visualization tools: http://selenic.com/repo/pagemap

2.6.26 kernel highlights

KGDB Finally have a mainlined in-kernel debugger

Some clock framework, clock driver and CPUfreq stuff on ARM

Coming in 2.6.27

FTrace? Anyone…, anyone…?

Technology Review

Bootup Time System Size File Systems Tracing Security Power Management Real-Time Middleware

Bootup Time

Async initlevels New patch by Arjan van de Ven Puts some driver initialization in parallel with other

boot tasks See http://lkml.org/lkml/2008/7/18/488

Size

Linux-tiny Recently got CONSOLE_TRANSLATIONS mainlined Next logical patches are ETHTOOL and IGMP

Bloatwatch 2.0 At ELC 2008 (April), Matt Mackall released Bloatwatch 2.0

Tool to show kernel size regression (and to investigate size problems)

See http://www.selenic.com/bloatwatch/

Function Sections (see next page)

Function Sections

"Function sections" is a technique for reducing the size of the kernel image

Consists of patches by Denys Vlasenko to support “gcc -ffunction-sections -fdata-sections” Places each function into it's own linker section This allows the linker to do better dead code removal

(using “ld –gc-sections”)

Denys reported that usage of this technique got him about a 10% reduction in kernel size (in some conditions)

File systems

SquashFS AXFS LogFS UBIFS

SquashFS

Compressed read-only file system, with smaller compression than CramFS

Latest release is 3.3, released Feb 5, 2008 Has been a flurry of recent activity, leading

up to Squashfs v. 4.0 Phillip Lougher is working to mainline it

CELF is working to fund this effort

AXFS

Advanced XIP file system Can profile applications, and only use XIP on

some blocks Allows for fine-grained control over how much

flash vs. RAM is used for an application set Go to OLS Session Friday at 11:00 am for

the latest info.

UBIFS

File system build on UBI (flash block) instead of block layer

Nokia recently (April) submitted v 3.0 for mainline inclusion http://lwn.net/Articles/276025

http://www.linux-mtd.infradead.org/doc/ubifs_whitepaper.pdf

LogFS

New flash filesystem by Jörn Engel to solve scalability problems with JFFS2

LogFS keeps filesystem meta-data on flash instead of in memory Does not need to read lots of meta-data on mount This reduces mount time (and system boot time) But, it has some outstanding problems

Tracing

FTrace LTTng (and Markers) SystemTap Printk-time arch support

Function Trace (ftrace)

Isolation and generalization of latency-trace system from RT-preempt patch Ingo Molnar and Steven Rostedt are primary developers

Compiler instrumentation of kernel functions (gcc -mcount)

Support for multiple tracers V16 submitted in mid-June

Already in linux-tip

I should put KFT on top of FTrace

Other Tracers

LTTng Status Markers infrastructure mainlined in 2.6.24 Next to mainline is actual LTTng core Go to OLS session Friday 10:00 for more info

SystemTap Nice system, but compilation step was not cross-compile aware

Lineo Solutions has demonstrated support for cross-execution! Work needed for embedded platforms (e.g. Kprobes for MIPS) Go to OLS Session Thursday at 14:00 for a ScriptFest

Printk-times arch support Many platforms have bad timer resolution for printk times

Security

LSM framework removed from kernel in 2.6.24 Has some impact on non-mainlined security

systems Tomoyo Linux, App Amour

App Armour has more bad news AppArmour group was let go from Novell

See http://www.news.com/8301-13580_3-9796140-39.html

Embedded SELinux (see next page)

Embedded SELinux

There has been much progress recently to support SELinux in the embedded space

Requires filesytem with extended attributes Some flash filesystems do not support xattrs

Yuichi Nakamura has described an embedded configuration of SELinux in as little as 700K See OLS Session Friday at 14:00 for more

information

Power Management

Powertop Shows timers and power state durations

Need support for CPUIdle, in order to show C-state (power state) activity for non-Intel processors

Richard Woodruff did support for TI OMAP (Hey other semi-conductor vendors, what are YOU

doing??) Clock Frameworks – need more arch support Wolfson voltage regulator stuff See ELC talks for presentations on all of the above

– http://www.embeddedlinuxconference.com/

RealTime

RT-preempt Latency tracer is being pushed to mainline Remaining large pieces seem to have stalled getting to

mainline: Threaded interrupts Sleeping spinlocks

Always needs tuning to make it work on a new platform Tuning notes published at ELC 2008 (Frank Rowand)

Xenomai emulation layer for legacy RTOS application support

Middleware

DLNA CELF hosted the first ever open source DLNA

summit, in Linz Austria CELF has donated several DLNA specifications to

open source projects New dlna-dev mailing list In process of obtaining sample hardware for

various DLNA projects DLNA summit #2 planned for ELC-Europe 2008

Mobile Phone News Open Handset Alliance and Android platform

Still waiting for deployment in phones LIMO

Feb 4 - announced their Linux platform Phones based on LIMO have shipped in Japan See LIMO press release

http://www.limofoundation.org/press-releases/limo-press-releases/limo-rolls-out-world-s-first-globally-competitive-linux-based-software-platform-for-mobile-devices.html

OpenMoko becoming available See Thursday Keynote – 16:00

Nokia buys out Symbian with plans to make it available as open source (!!?)

Status Resources LinuxDevices.com

http://www.linuxdevices.com/ LWN.net kernel pages

http://lwn.net/Kernel/ Articles sorted by topic

http://lwn.net/Kernel/Index/ Linux Weather Forecast

http://www.linux-foundation.org/en/Linux_Weather_Forecast

Embedded Linux Wiki http://elinux.org/ http://elinux.org/Technology_Watch_List

Technology Watch List

CE Linux Forum maintains a list of technologies that we are "watching" Things we are interested in Kind of like the Kernel Weather Forecast, but with focus on

embedded

List is reported on and updated at CELF meetings Page is on elinux wiki:

http://elinux.org/Technology_Watch_List Page is now up-to-date (mostly)

Open Discussion

Topics?Taking control of the kernel from

desktop and enterprise guysMy favorite quote this week from a

mainframe guy: “Sorry for all the bloat the last couple of years…”

…

Thanks!

You’re all invited to come to the CELF Embedded Developer BOF

At the Westin Hotel

Friday, July 25, 7:00 pm

There will be prizes!!! (but no food )