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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. Signed-off-by: Tejun Heo <tj@kernel.org> [ Added cfs_rq_is_decayed() ] Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Vincent Guittot <vincent.guittot@linaro.org> Cc: Chris Mason <clm@fb.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Paul Turner <pjt@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20170426004350.GB3222@wtj.duckdns.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.