LCU14 BURLINGAME

Mark Brown, LCU14

LCU14-511: LSK Overview & Update

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● Goals● Current status● Expected workflow● Discussion

Agenda

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● Share engineering effort for backports of common features○ Get key new features into production sooner○ Focus on shared engineering, provide a basis for vendor kernels○ One place to get many backports

■ Synchronize with a single tree■ Pre-integrated

● Provide QA and support

● Help feed experience from productization back into development

LSK Goals - Value proposition

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● Core, Android and RT flavours○ Android & RT flavours created to minimise disruption

● v3.10 on release○ New features until at least 14.12○ Support until 15.12

● v3.14 on release○ New features until at least 15.08○ Support until 16.08

Current status

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● Latest LTS release bug fixes from kernel.org● big.LITTLE GTS (v3.10 only) and IKS (ARMv7 only)● Power efficient workqueues● Gator ● Android enhancements● TC2 support● Big endian● pinctrl groups● Compressed audio framework enhancements● Warning fixes

ARMv7/ARMv8 features

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● Goal is to backport essentially all ARMv8 development upstream:○ CPU idle○ CPU suspend○ CPU topology○ Cryptography extensions○ Huge pages○ ftrace○ KGDB○ perf○ CMA○ Optimisations, fixes, smaller features

ARMv8 features

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1. Feature request discussed with LSK teama. Contact LSK team and/or member services to discuss any requirements

2. Feature approved for inclusion3. Feature team/LSK team prepares LSK backport4. LSK team reviews and merges backport5. BSP or other user team merges LSK into their kernel

a. Either tagged release or any other commit on the branchb. Branch is fast forward only, easily merged with git merge

6. End system integrator merges or uses BSP kernel

Expected workflow for users

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● Get code prepared for each LSK release○ Ideally prepared by people working directly in this area (eg, ARM for HMP)○ Otherwise LSK team monitors upstream development and backports○ v3.10 and v3.14 maintained in parallel, same updates to each

● Review code○ LSK team in conjunction with relevant domain experts within Linaro

● Submit code for pre-merge testing○ Duplicates LSK CI loops○ Reduces risk of regressions in main LSK tree

● Merge code into main LSK○ Code then goes into regular testing and will be part of routine release

Workflow for LSK team

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Web site: http://wiki.linaro.org/LSKgit tree: git://git.linaro.org/kernel/linux-linaro-stable.git

More information

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More about Linaro Connect: connect.linaro.org Linaro members: www.linaro.org/membersMore about Linaro: www.linaro.org/about/

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● Included in upstream kernel since v3.14● Simplest possible support

○ No scheduler modifications○ Pretends big cores are higher frequency states for little cores○ When little cores are too busy switches off little cores and moves all tasks to

big cores● Peak performance limited to big cores only● Not optimal for all workloads

○ eg, one compute intensive task and several low intensity tasks may be optimally supported with one big core and one little core

big.LITTLE IKS

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● Direct scheduler modification for big.LITTLE● Able to use big cores and little cores simultaneously

big.LITTLE GTS

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● Scheduler modifications for big.LITTLE being developed upstream● Still in development, not yet ready for production● Large changes for power management throughout the scheduler

big.LITTLE EAS/EES

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● ARMv8 support upstream still in development○ Key features like cpuidle still not merged for v3.17

● Urgent need for production● LSK team monitors upstream and backports as much as possible● Key out of tree features are also included

ARMv8 features

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● Feature backported base on LTS kernel v3.10/v3.14○ Feature branch can be used separately○ User can select needed features for specific board.

● Goal is complete feature parity, if support exists● i.e. features in LSK v3.10 are also in LSK v3.14

LSK feature branches