Messages in this thread | | | Subject | Re: [PATCH 1/3] sched/rt: cpupri_find: implement fallback mechanism for !fit case | From | Dietmar Eggemann <> | Date | Mon, 17 Feb 2020 20:09:24 +0100 |
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On 14/02/2020 17:39, Qais Yousef wrote:
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> /** > * cpupri_find - find the best (lowest-pri) CPU in the system > * @cp: The cpupri context > @@ -62,80 +115,72 @@ int cpupri_find(struct cpupri *cp, struct task_struct *p, > struct cpumask *lowest_mask, > bool (*fitness_fn)(struct task_struct *p, int cpu)) > { > - int idx = 0; > int task_pri = convert_prio(p->prio); > + int best_unfit_idx = -1; > + int idx = 0, cpu; > > BUG_ON(task_pri >= CPUPRI_NR_PRIORITIES); > > for (idx = 0; idx < task_pri; idx++) { > - struct cpupri_vec *vec = &cp->pri_to_cpu[idx]; > - int skip = 0; > > - if (!atomic_read(&(vec)->count)) > - skip = 1; > - /* > - * When looking at the vector, we need to read the counter, > - * do a memory barrier, then read the mask. > - * > - * Note: This is still all racey, but we can deal with it. > - * Ideally, we only want to look at masks that are set. > - * > - * If a mask is not set, then the only thing wrong is that we > - * did a little more work than necessary. > - * > - * If we read a zero count but the mask is set, because of the > - * memory barriers, that can only happen when the highest prio > - * task for a run queue has left the run queue, in which case, > - * it will be followed by a pull. If the task we are processing > - * fails to find a proper place to go, that pull request will > - * pull this task if the run queue is running at a lower > - * priority. > - */ > - smp_rmb(); > - > - /* Need to do the rmb for every iteration */ > - if (skip) > - continue; > - > - if (cpumask_any_and(p->cpus_ptr, vec->mask) >= nr_cpu_ids) > + if (!__cpupri_find(cp, p, lowest_mask, idx)) > continue; > > - if (lowest_mask) { > - int cpu;
Shouldn't we add an extra condition here?
+ if (!static_branch_unlikely(&sched_asym_cpucapacity)) + return 1; +
Otherwise non-heterogeneous systems have to got through this for_each_cpu(cpu, lowest_mask) further below for no good reason.
> + if (!lowest_mask || !fitness_fn) > + return 1; > > - cpumask_and(lowest_mask, p->cpus_ptr, vec->mask); > + /* Ensure the capacity of the CPUs fit the task */ > + for_each_cpu(cpu, lowest_mask) { > + if (!fitness_fn(p, cpu)) > + cpumask_clear_cpu(cpu, lowest_mask); > + }
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