sf00168887: cfs_rq clean backported from Tejun

PPA description

    sched/fair: Fix O(nr_cgroups) in load balance path

    Currently, rq->leaf_cfs_rq_list is a traversal ordered list of all
    live cfs_rqs which have ever been active on the CPU; unfortunately,
    this makes update_blocked_averages() O(# total cgroups) which isn't
    scalable at all.

    This shows up as a small CPU consumption and scheduling latency
    increase in the load balancing path in systems with CPU controller
    enabled across most cgroups. In an edge case where temporary cgroups
    were leaking, this caused the kernel to consume good several tens of
    percents of CPU cycles running update_blocked_averages(), each run
    taking multiple millisecs.

    This patch fixes the issue by taking empty and fully decayed cfs_rqs
    off the rq->leaf_cfs_rq_list.

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sudo add-apt-repository ppa:mimi0213kimo/cfs-rq-clean
sudo apt-get update
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deb http://ppa.launchpad.net/mimi0213kimo/cfs-rq-clean/ubuntu trusty main 
deb-src http://ppa.launchpad.net/mimi0213kimo/cfs-rq-clean/ubuntu trusty main 
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linux-lts-xenial 4.4.0-112.135~14.04.1hf00178886v20180206b0h51a05e6d6e6dhf00178886v20180206b0hca47fc49e267 (Newer version available) Gavin Guo ()
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