As a first step this patch makes cfs_tasks list as MRU one. It means, that when a next task is picked to run on physical CPU it is moved to the front of the list. Therefore, the cfs_tasks list is more or less sorted (except woken tasks) starting from recently given CPU time tasks toward tasks with max wait time in a run-queue, i.e. MRU list. Second, as part of the load balance operation, this approach starts detach_tasks()/detach_one_task() from the tail of the queue instead of the head, giving some advantages: - tends to pick a task with highest wait time; - tasks located in the tail are less likely cache-hot, therefore the can_migrate_task() decision is higher. hackbench illustrates slightly better performance. For example doing 1000 samples and 40 groups on i5-3320M CPU, it shows below figures: default: 0.657 avg patched: 0.646 avg Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Kirill Tkhai <tkhai@yandex.ru> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Mike Galbraith <umgwanakikbuti@gmail.com> Cc: Nicolas Pitre <nicolas.pitre@linaro.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com> Cc: Paul Turner <pjt@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tim Chen <tim.c.chen@linux.intel.com> Link: http://lkml.kernel.org/r/20170913102430.8985-2-urezki@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Change-Id: Id44ee1af4d88a01db1994e642518b7e3cc58f937 Signed-off-by: Danny Lin <danny@kdrag0n.dev> Signed-off-by: Alexander Winkowski <dereference23@outlook.com>fourteen
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