LCA13: big.LITTLE MP Updates
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Resource: LCA13 Name: big.LITTLE MP Updates Date: 04-03-2013 Speaker: Vincent Guittot
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LCA13: big.LITTLE MP Updates
- 1. ASIA 2013 (LCA13) big.LITTLE update Power Management Working Group - v2 Vincent Guittot / Amit Kucheria / Morten Rasmussen
- 2. ASIA 2013 (LCA13) www.linaro.org Content Status Policy Patches Open issues Details
- 3. 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 tests Currently under review and test by ARM and Linaro 1st results are aligned with old HMP patches Available on git.linaro.org See patches section Few use cases need to be improved See open issues section
- 4. 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
- 5. ASIA 2013 (LCA13) www.linaro.org Patches : some fixes Fix nr_busy_cpus Remove spurious trig of Idle Load Balance https://lkml.org/lkml/2013/2/21/53 v5 under preparation Fix load_avg with -rt task Fix the load average tracking if only -rt tasks run on a core https://lkml.org/lkml/2013/2/13/71 Fix active migration Fix the target CPU of active load balance if only 1 task run on a core https://lkml.org/lkml/2013/2/12/158
- 6. ASIA 2013 (LCA13) www.linaro.org Patches : load balance (1/2) Pack small tasks Pack small tasks on few cores (A7 for b.L) http://lwn.net/Articles/528883/ v3 under test Use per task load average Weight the task contribution with the run time Only nice priority before Use LB_MIN feature Balance long running tasks in priority PST takes care of small task
- 7. ASIA 2013 (LCA13) www.linaro.org Patches : load balance (2/2) Migrate on CPU with highest capacity Use CPU with highest capacity Tune sched_domain for b.L Tunings for b.L platform Reduce Periodic load balance for responsiveness Scaling Invariance Ensure load invariance across core and running frequency Not available yet
- 8. 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_prio nice priority -20 @ 10% : 887 nice priority 0 @ 100% : 1024 nice 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 ?
- 9. ASIA 2013 (LCA13) www.linaro.org A15 cluster capacity 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 idle Example with sysbench and 5 threads T0 CPU1 T1 T2 A7 cluster capacity of 1883 CPU3 T3 CPU4 T4 CPU2
- 10. ASIA 2013 (LCA13) www.linaro.org Pack small tasks in details Pack small tasks on 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%
- 11. ASIA 2013 (LCA13) www.linaro.org Use best core in details Use the core with highest capacity Periodic load balance focuses long running tasks Ensure long running tasks are balanced in priority A15 A15 A7 A7 A7
- 12. ASIA 2013 (LCA13) www.linaro.org Bbench example Page rendering example with audio playback WebViewCore-Thread SurfaceFlinger Android.browser Audio Threads A15 A15 A7 A7 A7 A15 A15 A7 A7 A7
- 13. More about Linaro Connect: www.linaro.org/connect/ More about Linaro: www.linaro.org/about/ More about Linaro engineering: www.linaro.org/engineering/ ASIA 2013 (LCA13)