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Unlike running, the runnable part can't be directly propagated through the hierarchy when we migrate a task. The main reason is that runnable time can be shared with other sched_entities that stay on the rq and this runnable time will also remain on prev cfs_rq and must not be removed. Instead, we can estimate what should be the new runnable of the prev cfs_rq and check that this estimation stay in a possible range. The prop_runnable_sum is a good estimation when adding runnable_sum but fails most often when we remove it. Instead, we could use the formula below instead: gcfs_rq's runnable_sum = gcfs_rq->avg.load_sum / gcfs_rq->load.weight which assumes that tasks are equally runnable which is not true but easy to compute. Beside these estimates, we have several simple rules that help us to filter out wrong ones: - ge->avg.runnable_sum <= than LOAD_AVG_MAX - ge->avg.runnable_sum >= ge->avg.running_sum (ge->avg.util_sum << LOAD_AVG_MAX) - ge->avg.runnable_sum can't increase when we detach a task The effect of these fixes is better cgroups balancing. Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Ben Segall <bsegall@google.com> Cc: Chris Mason <clm@fb.com> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Josef Bacik <josef@toxicpanda.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Morten Rasmussen <morten.rasmussen@arm.com> Cc: Paul Turner <pjt@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Tejun Heo <tj@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Yuyang Du <yuyang.du@intel.com> Link: http://lkml.kernel.org/r/1510842112-21028-1-git-send-email-vincent.guittot@linaro.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.