lca13: big.little mp updates

ASIA 2013 (LCA13)

big.LITTLE updatePower Management Working Group - v2Vincent Guittot / Amit Kucheria / Morten Rasmussen

ASIA 2013 (LCA13)

www.linaro.org

Content

StatusPolicyPatchesOpen issuesDetails

ASIA 2013 (LCA13)

www.linaro.org

Status

Current Linaro kernel uses old HMP patches

New patches designed to not be HMP specific

Patches under internal review and testsCurrently under review and test by ARM and Linaro1st results are aligned with old HMP patches

Available on git.linaro.orgSee patches section

Few use cases need to be improvedSee open issues section

ASIA 2013 (LCA13)

www.linaro.org

Policy

As simple as 3 rules

Pack small tasks on LITTLE cores at wake up

Balance long running tasks in priority

Choose core with best capacity

ASIA 2013 (LCA13)

www.linaro.org

Patches : some fixes

Fix nr_busy_cpusRemove spurious trig of Idle Load Balancehttps://lkml.org/lkml/2013/2/21/53v5 under preparation

Fix load_avg with -rt taskFix the load average tracking if only -rt tasks run on a corehttps://lkml.org/lkml/2013/2/13/71

Fix active migrationFix the target CPU of active load balance if only 1 task run on a corehttps://lkml.org/lkml/2013/2/12/158

ASIA 2013 (LCA13)

www.linaro.org

Patches : load balance (1/2)

Pack small tasksPack small tasks on few cores (A7 for b.L)http://lwn.net/Articles/528883/v3 under test

Use per task load averageWeight the task contribution with the run timeOnly nice priority before

Use LB_MIN featureBalance long running tasks in priorityPST takes care of small task

ASIA 2013 (LCA13)

www.linaro.org

Patches : load balance (2/2)

Migrate on CPU with highest capacityUse CPU with highest capacity

Tune sched_domain for b.LTunings for b.L platformReduce Periodic load balance for responsiveness

Scaling InvarianceEnsure load invariance across core and running frequencyNot available yet

ASIA 2013 (LCA13)

www.linaro.org

Open issue: nice priority - load_avg_contrib

Nice priority define a “runtime slice allocation”

load_avg_contrib is %runnable x nice_prionice priority -20 @ 10% : 887nice priority 0 @ 100% : 1024nice priority 10 @ 100% : 110

What is the best place for :

A long running task with low priority ?AsyncTask in Android as an example

A short running tasks with high priority ?

ASIA 2013 (LCA13)

www.linaro.org

A15 clustercapacity of 2882

CPU0

Open issue: Offloading to A7

Use A7 instead of overloading A15

Load balance puts more tasks on A15 and let an A7 idleExample with sysbench and 5 threads

T0

CPU1

T1

T2

A7 clustercapacity of 1883

CPU3

T3

CPU4

T4

CPU2

ASIA 2013 (LCA13)

www.linaro.org

Pack small tasks in details

Pack small taskson LITTLE core for big.LITTLE

Powertop results for Android MP3 playback

A15 Cluster CPU0 CPU1

WFI 0% 0%

C1 99,4% 99,9%

A7 Cluster CPU2 CPU3 CPU4

WFI 0,2% 0,1% 0,0%

C1 80,1% 97,6% 98,2%

ASIA 2013 (LCA13)

www.linaro.org

Use best core in details

Use the core with highest capacity

Periodic load balance focuses long running tasksEnsure long running tasks are balanced in priority

A15

A15

A7

A7

A7

ASIA 2013 (LCA13)

www.linaro.org

Bbench example

Page rendering example with audio playback

WebViewCore-Thread

SurfaceFlinger

Android.browserAudio Threads

A15

A15

A7

A7

A7

A15

A15

A7

A7

A7

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ASIA 2013 (LCA13)