Status of Embedded Linux Embedded Linux Update 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 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

 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.)

 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/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 proposal for Alan Stern's  See http://lkml.org/lkml/2010/5/30/83 proposal for Mark Gross'

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=2e72b6347c9459e6cff5 634ddc815485bae6985f 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 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

   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 platforms  Seems 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!