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Embedded Linux Update June, 2010. Status of Embedded Linux. 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

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embedded linux update june 2010
Embedded Linux

Update

June, 2010

Status of Embedded Linux

Tim Bird

CELF Architecture Group Chair

outline
Outline
  • Kernel Versions
  • Technology Areas
  • Embedded Distributions
  • Resources
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
Linux v2.6.34
  • LogFS
  • Asynchronous Suspend/Resume
  • Memory threshold notifications for cgroups
linux v2 6 35 rc1 expected
Linux v2.6.35-rc1 (expected)
  • Ramoops driver
    • Records oops to persistent RAM so it can be recovered later
      • Maybe 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
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 coldboot
      • Depends 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
Patches to watch (cont.)‏
  • Suspend blockers
    • Android opportunistic suspend patches (successor to wake locks)
      • More on this later
technology areas1
Technology Areas
  • File Systems
  • Power Management
  • Real-time
  • System Size
  • Tracing
file systems
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
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 cont1
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 cont2
File systems (cont.)
  • LogFS is new, and it really needs testing
    • Please try it out and report back!
power management
Power Management
  • Suspend Blockers submission by Google
    • Successor to wake locks
    • Lots of discussion – no resolution yet
      • See http://lwn.net/Articles/388131
      • and http://lwn.net/Articles/389407
      • And 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 kernel
      • See http://lkml.org/lkml/2010/5/29/77 for Alan Stern's proposal
      • See http://lkml.org/lkml/2010/5/30/83 for Mark Gross' proposal
real time
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
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
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 cont1
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 removed
      • http://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
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
android
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
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
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
  • 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
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
New Consortium
  • Linaro
    • http://www.linaro.org/
    • Focused on technologies and improvements of Linux for ARM platforms
      • Seems like “CELF for ARM”
    • It’s not entirely clear exactly what they are going to do
resources
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