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Software and Services Group
Embedded Linux and the mainline kernelDavid Woodhouse
CELF Embedded Linux Conference
April 2009
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Ubiquitous Linux
Embedded control device... phone... PDA... Internet tablet... router...media device... netbook... laptop... desktop... server... supercomputer...
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“Embedded”...?
Portable Media Players
Phones
PDAs
“Internet Tablets”
Routers
Televisions
VCR / PVR / DVD / Media
Netbooks (?)
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“Embedded”...?
Headless?
Handheld?
Power source?
Physical size?
Limited RAM?
Storage?
Other...
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Embedded needs
Power management
Fast startup
Headless operation
Uncluttered user interfaces
Solid state storage
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Embedded needs
Power management
Fast startup
Headless operation
Uncluttered user interfaces
Solid state storage
Other users need these features too!
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Power Management
Battery life
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Power Management
Battery life
Cost of power consumption
Heat output
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Tickless operation
Power savings
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Tickless operation
Power savings
Scalability for virtualisation
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Fast boot
Hard limits for mobile telephones
User experience for consumer electronics
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Fast boot
Hard limits for mobile telephones
User experience for consumer electronics
Server availability
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User interfaces
Ease of use for consumer equipment
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User interfaces
Ease of use for consumer equipment
... and for everyone else:OLPC / Sugar
Netbooks
Simple desktop environments
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Solid state storage
FLASH storage in “embedded” devices
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Solid state storage
FLASH storage in “embedded” devices
Solid State Disk
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Others...
Execute in place (XIP)From FLASH for embedded systems
Shared file system data under virtualisation
DMA API usageFor cache coherency on embedded systems (ARM, some PPC)
For IOMMU on larger systems
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We are not so special!
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Community impressions
“Enterprise” Linux
“Embedded” Linux
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Community impressions
“Enterprise” Linux
“Embedded” LinuxWorking with old code
Not working with upstream
Inclined towards “special” one-off hacks
Irrelevant to the general case
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Community impressions
“Enterprise” Linux
“Embedded” LinuxWorking with old code
Not working with upstream
Inclined towards “special” one-off hacks
Irrelevant to the general case
We must prove them wrong!
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“Embedded” success stories
Tickless
Preemptive kernel
Power management
Suspend to RAM
Solid state storage
Squashfs
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Working with the community
Find generic points of interest
Publish early and oftenIn git trees
Separate trees for separate development efforts
Also send patches for review
Solicit and respond to feedback
Work with upstream maintainers
BE PART OF THE COMMUNITY!
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Staying close to upstream
AdvantagesEasier for product updates and new products
Easy to use fixes and new features
External contributions
Code review and testing
CostsWriting acceptable code can be hard and takes time
Upstream kernel is a fast-moving target
Releasing information may be difficult
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Tips on contributing code
Find parallel requirements
Avoid “hacking around” problems
Avoid overengineering
Care about locking
Coding Style
Submit patches carefully
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What's next for “Embedded” Linux?
Solid state storageMore work on SSDs
Flash file system development (UBI, logfs, btrfs)
Better power management
More real time development
What do you need?
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Questions?
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