Add support for cpu hotplug on ARM

Registered by Amit Kucheria on 2010-10-04

This blueprint has been superseded. See the newer blueprint "Hotplug Performance Improvements" for updated plans.

Infrastructure code to pull power gated CPUs in and out of actions

 * hotplug is a very expensive operation - might not make sense for low-latency transitions

Blueprint information

Amit Kucheria
Amit Kucheria
Vincent Guittot
Series goal:
Accepted for 11.05
Milestone target:
milestone icon 11.05-04
Started by
Amit Kucheria on 2010-11-02
Completed by
Amit Kucheria on 2012-10-09

Related branches



[amitk: 2/11/2010]
 * At LDS, it was decided to implement the functionality to allow hotpluging of cores, but leave the question of when to do it to policy
 * If possible, common code will be identified and the implementations refactored

[vingu: 19/11/2010 - 09/12/2010]

link to the wiki page :

Regarding blocked item:
 *cpu hotplug trace events patch is under review
 *cpu hotplug plugin for pytimechart will be submitted only when a trace event patch will be accepted

In progress


Work Items

Work items:
[vincent-guittot] Make a status of the hotplug feature on a CA9 based SoC (MOP U8500): DONE
[vincent-guittot] Implement patch for a functional hotplug feature on MOP U8500 if necessary: DONE
[vincent-guittot] Check/Split common and SoC specific code: DONE
[vincent-guittot] Push a patch to the linux-arm-kernel if necessary: DONE
[vincent-guittot] Add some traces events if necessary: BLOCKED
[vincent-guittot] Define some hotplug latency measurement test cases: DONE
[lnxtorez] Integrate Vincent's hotplug tests in testing infrastructure: DONE
[vincent-guittot] Perform hotplug latency measurements on ST-E MOP U8500: DONE
[vincent-guittot] Identify/study high latency root cause: DONE
[vincent-guittot] study for high latency solution: DONE
[vincent-guittot] Define hotplug retention measurement test cases: DONE
[vincent-guittot] Perform hotplug retention measurements on MOP U8500: DONE
[vincent-guittot] Add a cpu hotplug plugin to pytimechart: BLOCKED
[vishwanath-bs] Perform hotplug latency measurements on TI OMAP4: DONE
[amitdanielk] Perform hotplug latency measurements on Samsung Orion: DONE
[vincent-guittot] Check Mike Turquette's patch for cpufreq governor-based hotplugging: DONE

Work items for backlog:
[amitk] Review the latency test cases: POSTPONED
[amitk] Review the interesting test usecases: POSTPONED
[sjahnke] Drive towards a solution for hotplug usage policy: POSTPONED
[vincent-guittot] Compute results and define a hotplug usage policy: POSTPONED
[vincent-guittot] Test the hotplug policy with some stress cases: POSTPONED
[amitdanielk] Perform hotplug retention measurements on Orion: POSTPONED

Dependency tree

* Blueprints in grey have been implemented.

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