From 23e71d8ba42933bff12e453858fd68c073bc5258 Mon Sep 17 00:00:00 2001 From: Luca Abeni Date: Wed, 20 May 2020 15:42:43 +0200 Subject: [PATCH] sched/deadline: Implement fallback mechanism for !fit case When a task has a runtime that cannot be served within the scheduling deadline by any of the idle CPU (later_mask) the task is doomed to miss its deadline. This can happen since the SCHED_DEADLINE admission control guarantees only bounded tardiness and not the hard respect of all deadlines. In this case try to select the idle CPU with the largest CPU capacity to minimize tardiness. Favor task_cpu(p) if it has max capacity of !fitting CPUs so that find_later_rq() can potentially still return it (most likely cache-hot) early. Signed-off-by: Luca Abeni Signed-off-by: Dietmar Eggemann Signed-off-by: Peter Zijlstra (Intel) Acked-by: Juri Lelli Link: https://lkml.kernel.org/r/20200520134243.19352-6-dietmar.eggemann@arm.com --- kernel/sched/cpudeadline.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c index 8630f2a..8cb06c8 100644 --- a/kernel/sched/cpudeadline.c +++ b/kernel/sched/cpudeadline.c @@ -121,19 +121,31 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p, if (later_mask && cpumask_and(later_mask, cp->free_cpus, p->cpus_ptr)) { - int cpu; + unsigned long cap, max_cap = 0; + int cpu, max_cpu = -1; if (!static_branch_unlikely(&sched_asym_cpucapacity)) return 1; /* Ensure the capacity of the CPUs fits the task. */ for_each_cpu(cpu, later_mask) { - if (!dl_task_fits_capacity(p, cpu)) + if (!dl_task_fits_capacity(p, cpu)) { cpumask_clear_cpu(cpu, later_mask); + + cap = capacity_orig_of(cpu); + + if (cap > max_cap || + (cpu == task_cpu(p) && cap == max_cap)) { + max_cap = cap; + max_cpu = cpu; + } + } } - if (!cpumask_empty(later_mask)) - return 1; + if (cpumask_empty(later_mask)) + cpumask_set_cpu(max_cpu, later_mask); + + return 1; } else { int best_cpu = cpudl_maximum(cp); -- 2.7.4