sched/fair: Search a task from the tail of the queue
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>
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parent
051f3ca02e
commit
93824900a2
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@ -6628,10 +6628,7 @@ again:
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set_next_entity(cfs_rq, se);
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set_next_entity(cfs_rq, se);
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}
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}
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if (hrtick_enabled(rq))
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goto done;
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hrtick_start_fair(rq, p);
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return p;
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simple:
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simple:
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#endif
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#endif
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@ -6645,6 +6642,16 @@ simple:
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p = task_of(se);
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p = task_of(se);
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done: __maybe_unused
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#ifdef CONFIG_SMP
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/*
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* Move the next running task to the front of
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* the list, so our cfs_tasks list becomes MRU
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* one.
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*/
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list_move(&p->se.group_node, &rq->cfs_tasks);
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#endif
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if (hrtick_enabled(rq))
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if (hrtick_enabled(rq))
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hrtick_start_fair(rq, p);
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hrtick_start_fair(rq, p);
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@ -7080,11 +7087,12 @@ static void detach_task(struct task_struct *p, struct lb_env *env)
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*/
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*/
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static struct task_struct *detach_one_task(struct lb_env *env)
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static struct task_struct *detach_one_task(struct lb_env *env)
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{
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{
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struct task_struct *p, *n;
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struct task_struct *p;
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lockdep_assert_held(&env->src_rq->lock);
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lockdep_assert_held(&env->src_rq->lock);
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list_for_each_entry_safe(p, n, &env->src_rq->cfs_tasks, se.group_node) {
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list_for_each_entry_reverse(p,
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&env->src_rq->cfs_tasks, se.group_node) {
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if (!can_migrate_task(p, env))
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if (!can_migrate_task(p, env))
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continue;
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continue;
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@ -7130,7 +7138,7 @@ static int detach_tasks(struct lb_env *env)
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if (env->idle != CPU_NOT_IDLE && env->src_rq->nr_running <= 1)
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if (env->idle != CPU_NOT_IDLE && env->src_rq->nr_running <= 1)
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break;
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break;
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p = list_first_entry(tasks, struct task_struct, se.group_node);
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p = list_last_entry(tasks, struct task_struct, se.group_node);
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env->loop++;
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env->loop++;
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/* We've more or less seen every task there is, call it quits */
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/* We've more or less seen every task there is, call it quits */
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@ -7180,7 +7188,7 @@ static int detach_tasks(struct lb_env *env)
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continue;
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continue;
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next:
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next:
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list_move_tail(&p->se.group_node, tasks);
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list_move(&p->se.group_node, tasks);
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}
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}
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/*
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/*
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