Status of Embedded Linux

Embedded LinuxUpdate

June, 2010

Tim Bird

CELF Architecture Group Chair

Outline

Kernel Versions Technology Areas Embedded Distributions Resources

Linux Kernel Versions

Kernel Versions

Linux v2.6.30 – 10 June 2009 Linux v2.6.31 – 9 Sep 2009 Linux v2.6.32 – 2 Dec 2009 Linux v2.6.33 – 24 Feb 2010 Linux v2.6.34 – 16 May 2010

5 kernels in 11 months Linux v2.6.35 merge window just closed

2.6.35-rc1 – 30 May 2010

Linux v2.6.34

LogFS Asynchronous Suspend/Resume Memory threshold notifications for cgroups

Linux v2.6.35-rc1 (expected)

Ramoops driver Records oops to persistent RAM so it can be

recovered laterMaybe obsoletes pramfs?

http://lwn.net/Articles/377890 Tracepoint size reduction

Shrinks size of kernel with tracepoints turned on by about 100K

http://lwn.net/Articles/386331 Section renaming to support –ffunction-

sections

Patches to watch

Speed up symbol resolution during module loading Sorts symbol table and avoid linear lookup cost

per symbol when loading a module Developer, Alan Jenkins, reports saving 20% of

time on coldbootDepends on modules being loaded

Did not make it into 2.6.33 Alan said he’ll try to mainline it again

Patches to watch (cont.)

Suspend blockers Android opportunistic suspend patches

(successor to wake locks)More on this later

Technology Areas

Technology Areas

File Systems Power Management Real-time System Size Tracing

File Systems

SquashFS Patches for LZMA support were submitted to

kernel mailing list in late 2009, but they missed the merge window See http://lkml.org/lkmlk/2009/12/10/456 Linus wants lzma library access refactored

LGE (Chan Jeong) recently submitted patches for LZO support Phillip said he'd mainline them See http://old.nabble.com/-PATCH-1-2--

Squashfs:-add-LZO-decompression-support-to28591383.html

File systems (cont.)

UBIFS Toshiba has reported on performance of this LGE says they are using UBIFS in product, in

part because it boots faster than YAFFS2 CELF has contracted with Free Electrons to

measure UBIFS mount times and find problem areas

File systems (cont.)

LogFS Log-structured file system which keeps meta-data on flash

Mounts really fast (no need to build in-memory tables to start accessing)

http://www.logfs.org/ Also Documentation/filesystems/logfs.txt

Mainlined (after much work) in 2.6.34 CELF supported this a few years ago Introduction

http://lwn.net/Articles/234441/ Announcement of mainlining

http://lwn.net/Articles/377741

File systems (cont.)

LogFS is new, and it really needs testing Please try it out and report back!

Power Management

Suspend Blockers submission by Google Successor to wake locks Lots of discussion – no resolution yet

See http://lwn.net/Articles/388131and http://lwn.net/Articles/389407And especially http://lwn.net/Articles/390392

Last thing I saw were counter-proposals to utilize PM QOS system to push some “suspend blocker” functionality outside of kernelSee http://lkml.org/lkml/2010/5/29/77 for Alan Stern's

proposalSee http://lkml.org/lkml/2010/5/30/83 for Mark Gross'

proposal

Real-time

Work continues on improving RT performance on embedded platforms

General work lately consists of removing Big Kernel Lock CELF considered funding this, but it looks like it

will happen without a funded project See http://lwn.net/Articles/380174/

Frank Rowand has good information about using RT-preempt See Frank’s presentation from ELC 2010: http://elinux.org/images/b/be/Real_time_linux_failure.pdf

More info coming to eLinux wiki soon!

System Size / Memory

Compression LZO kernel image compression It was merged in 2.6.33

Ramzswap – (aka compcache) made the 2.6.33 merge window See http://lwn.net/Articles/334649

System Size / Memory (cont.)

Memory threshhold notifications in cgroups: Can use cgroups to get notifications of

memory problems on a per-app or app-group basis

Merged in 2.6.34 http://git.kernel.org/?p=linux/kernel/git/

torvalds/linux-2.6.git;a=commitdiff;h=2e72b6347c9459e6cff5634ddc815485bae6985f

See Documentation/cgroups/memory.txt

System Size / Memory (cont.)

New allocator “SLEB” was proposed SLEB was rejected

Linus says he won't take a new allocator until another one is removedhttp://lwn.net/Articles/389402/

New plan is to incrementally improve SLAB, if possible, while trying to avoid regressions http://thread.gmane.org/

gmane.linux.kernel.mm/48515

Tracing

Ftrace Proposal to merge ftrace and perf ring-buffer code

Ingo not very enthusiastic Lots of code may move from ftrace to perf

http://lwn.net/Articles/388978/ Trace-cmd and kernelshark

New command line and GUI tools See presentations from ELC and Collab summit

Perf Support for data interpretation on a different machine

“perf archive” CELF project to create a trace format data standard

Embedded Distributions

Android

Android 2.1 SDK (Eclair) released (28 Oct 2009) Number of devices still increasing

Non-phones starting to appear (tablets and TVs) Google TV / Sony Internet TV

Android patches removed from mainline kernel (2.6.33) Greg Kroah-Hartman talked about this at ELC

http://elinux.org/images/c/ca/Gregkh-android-presentation-kernel.pdf

Google and kernel developers had private meeting at Collaboration Summit, and hashed out some issues

Android (cont.)

Froyo (v2.2) features discussed at Google I/O Dalvik now has a Just-In-Time compiler

“Froyo runs apps up to 450% faster” (really?) Actual Google I/O demo of popular game looked

about 40% faster (in terms of frames per second) Still very good

Flash support WiFi tethering Batch app upgrade Faster Javascript

Meego

Moblin + Maemo = Meego Intel and Nokia joining forces to create single

embedded distribution See http://meego.com/

Lots of stuff about this at ELC and Collab summit

Early (partial) release was March 31 Full release of Meego 1.0 was May 25

Ubuntu

Ubuntu netbook Now working towards targeting ARM Some rumors of them support Android apps Canonical is working to support appliances Have new “Unity” netbook interface

“Ubuntu Light” targeted at instant-on

WebOS

HP buys Palm and now owns WebOS OS used on current Palm Pre Expected to ship on tablets by end of year

I haven’t seen an WebOS opensource site

New Consortium

Linaro http://www.linaro.org/ Focused on technologies and improvements of

Linux for ARM platformsSeems like “CELF for ARM”

It’s not entirely clear exactly what they are going to do

Resources

LWN.net http://www.lwn.net/ If you are not a subscriber, please do so This is an invaluable community resource that

needs your support Prices just went up a bit ($7 per month vs. $5 per

month for professional subscription) eLinux wiki

http://elinux.org/ Linux-embedded mailing list

http://vger.kernel.org/vger-lists.html#linux-embedded

Thanks!