SonyMEI Collaboration Source Tree Overview

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Sony/MEI CollaborationSource Tree Overview

• Tim Bird
• Sony Electronics Inc.
• Co-Chair of the CE Linux Forum
• Architecture Group

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Source Tree Status

• Based on Linux kernel version 2.4.20
• Has support for ARM and MIPS architectures
• Based on MontaVista CE Edition version 3.x

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Patch metrics

• Size of Patch (as of June 13) 58 meg.
• Diffstat
• 5939 files changed
• 951,072 insertions
• 868,691 deletions
• Thats the bad news!

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Patch overview

• Its not as bad as it looks
• Many of the deletions (95) are from removal of
  /arch directories
  
• 820,879 deletions in arch directories
• Lots of additions are in /arch/arm and
  /arch/mips
  
• 150,000 insertions
• Ignoring these, patch size is comparable to diff
  for average distribution of Linux
  
• E.g. RedHat 9.0 has about 23 meg. of diff vs. its
  base kernel

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Major Area Categories

• Two major categories of changes
• MontaVista CE Edition baseline changes
• Changes specifically for the Sony/MEI
  collaboration project
  
• In general, almost every change is configurable
  via a CONFIG_xxx option

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List of requested technologies

• Preemptible kernel
• Lock-break
• O(1) Scheduler
• Parallel and deferred I/O initialization
• BH processing elimination
• High resolution timers

• Execute-in-place (XIP)
• Power Management Framework
• CPU Frequency Scaling
• Clock rate change on non-preemptible regions
• Deferred periodic kernel process
• Protected RAM FS

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Resources for StudyingSelected Technologies
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Important Note!

• This presentation mostly has information about
  parts of code that are available in open source
  
• Other parts of code will be available soon
• In some cases, code has been backported from 2.5
  to 2.4 kernel (Its availabe for 2.5, but not for
  2.4, publicly)

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Preemptible kernel

• Was accepted in kernel in 2.5.4-pre6
• Early interview with Robert Love at
  http//www.linuxdevices.com/articles/AT8267298734.
  html
  
• Very early overview article is athttp//www.linu
  xdevices.com/articles/AT4185744181.html
  
• Project home page is athttp//kpreempt.sourcefor
  ge.net/
  
• Publicly available patch at ftp//ftp.kernel.org/
  pub/linux/kernel/people/rml/preempt-kernel/v2.4/

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Preemptible Kernel (cont.)

• See also
• /Documentation/preempt-locking.txt
• Main files are
• include/linux/spinlock.h
• kernel/sched.c
• arch/arm/kernel/entry-armv.S

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Lock-break

• Author is Robert Love
• Publicly available README is at
  ftp//ftp.kernel.org/pub/linux/kernel/people/rml/l
  ock-break/README-lock-break
  
• Publicly available patch is at
  ftp//ftp.kernel.org/pub/linux/kernel/people/rml/l
  ock-break/v2.4/

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Lock-break (cont.)

• Main file is
• include/lock_break.h
• Also useful to walk through
• lock_break_rml_2.4.18-1.patch
• Look for long-held kernel locks that this patch
  breaks

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O(1) Scheduler

• Author is Ingo Molnar
• Article about it is at http//www.hpl.hp.com/rese
  arch/linux/kernel/o1.php
  
• Some published benchmark results are at
  http//kerneltrap.com/node.php?id343
  
• Some background, and insertion
  announcements http//kerneltrap.org/node.php?id
  187
  
• Publicly available patch is available
  at http//people.redhat.com/mingo/O(1)-scheduler
  /sched-2.4.19-rc2-A4

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O(1) Scheduler (cont.)

• Main file is
• kernel/sched.c

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Work queues(Part of BH elimination)

• Workqueues accepted in kernel at 2.5.40
• Replaces task queues
• LWN article is at http//lwn.net/Articles/10963/
  
• Main file is
• kernel/workqueue.c

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High resolution timers

• Project home page is athttp//sourceforge.net/pr
  ojects/high-res-timers
  
• Main file is
• kernel/itimer.c

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Execute-in-place (XIP)

• Main files are
• arch/arm/kernel/setup.c
• arch/arm/mach-omap1510/innovator.c
• arch/arm/mm/init.c
• Assembly language files
• arch/arm/kernel/entry-common.S
• arch/arm/kernel/head-armv.S
• Linker script
• arch/arm/vmlinux-armv-xip.lds.in
• See also arch/arm/Makefile
• Grep for CONFIG_XIP_ROM

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Power Management Framework

• Framework code is in drivers/dpm
• Main files are
• drivers/dpm/dpm.c
• drivers/dpm/dpm-syscall.c
• drivers/dpm/dpm-idle.c

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Change clock rate in non-preemptible regions

• Main files are
• fs/devices.c
• fs/namei.c
• include/asm-arm/arch-omap1510/omap1510_dpm.h
• mm/memory.c,
• arch/arm/config.in
• arch/arm/mach-omap1510/omap1510_dpm.c

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Deferred periodic kernel process

• Related materials
• Software Matters for Power Consumption
• http//www.embedded.com/story/OEG20030121S0057
• Main files
• arch/arm/mach-omap1510/pm.c
• kernel/timer.c
• Grep for CONFIG_VST

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Protected RAM FS

• Original work was nvrd
• nvrd project home page is at http//www.savan.co
  m/erez/nvrd.html
  
• Main file is
• drivers/block/nvprd.c

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Other Resources

• Founding members will publish an article on July
  7th in Nikkei EL, with information about the
  collaboration project

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Other Stuff in the Source Tree
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Other Stuff in the Source Tree

• Since code is based on MontaVista CE Edition,
  there are many additional items which are not
  related to the Sony/MEI collaboration project
  
• Many of these items are also good for embedded
  Linux projects
  
• Things that are unrelated to embedded use of
  Linux are configurable (can be turned off)

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List of Other Stuff in the Source

• Support for Xilinx, Altera, and other FPGA
  devices
  
• Lots of ARM board support packages
• Lots of MIPS board support packages
• lm_sensors patch (it's also in rh-2.4.20-8)
• More supported buses
• L3 (3-wire serial), VME, maple, spi, ssi
• Device USB support

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Other Stuff (cont.)

• Sysfs (backport of early 2.5 version)
• Inflatefs
• Nvramfs
• FS Quota support
• XFS journaling file system
• Posix message queue FS (not finished)
• Preemption latency measurement tools

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Other Stuff (cont.)

• Some ha (high availability) materials
• IPSec
• IPv6 enhancements
• POSIX Access Control Lists (ACLs)
• Zlib
• Cryptographic API

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Problems to consider

• Support for other architectures will require some
  work
  
• Some patches applied by MontaVista also affect
  other architectures (e.g. files in /arch/i386/)
  
• MontaVista has excluded those /arch directories
  from this release
  
• This will require some back-porting, or
  reapplication of certain patches for these
  architectures

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Problems (cont.)

• Patches are not currently broken into individual
  parts
  
• Need to consider how and when to synchronize with
  kernel.org tree

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Relationship between collaboration project and
other Linux trees
Sony Matsushita Joint Development
Additional Sony/MEI work
Current Sony/MEI project
MVL 3.0CE
Kernel.org 2.4.20
Kernel.org 2.6?
CE Linux Forum Source Tree
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What to do next?

• This presentation will be sent to you
• You can use this presentation to review public
  materials in advance of receiving the source
  code
  
• When you get the code, examine the identified
  files, in detail
  
• Also, looking at a diff of Documentation/Configure
  .help is helpful
  

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Q A