Messages in this thread Patch in this message | | | From | Dietmar Eggemann <> | Subject | [PATCH 4/4] sched/deadline: Implement fallback mechanism for !fit case | Date | Wed, 8 Apr 2020 11:50:12 +0200 |
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From: Luca Abeni <luca.abeni@santannapisa.it>
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.
Signed-off-by: Luca Abeni <luca.abeni@santannapisa.it> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> --- kernel/sched/cpudeadline.c | 19 +++++++++++++++---- 1 file changed, 15 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c index 8630f2a40a3f..8525d73e3de4 100644 --- a/kernel/sched/cpudeadline.c +++ b/kernel/sched/cpudeadline.c @@ -121,19 +121,30 @@ 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 = arch_scale_cpu_capacity(cpu); + + if (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); -- 2.17.1
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