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SubjectRe: [PATCH V2 2/7] cpuset: Rebuild root domain deadline accounting information
On 2 February 2018 at 05:52, Juri Lelli <juri.lelli@redhat.com> wrote:
> Hi Mathieu,
>
> On 01/02/18 09:51, Mathieu Poirier wrote:
>> When the topology of root domains is modified by CPUset or CPUhotplug
>> operations information about the current deadline bandwidth held in the
>> root domain is lost.
>>
>> This patch address the issue by recalculating the lost deadline
>> bandwidth information by circling through the deadline tasks held in
>> CPUsets and adding their current load to the root domain they are
>> associated with.
>>
>> Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
>> ---
>
> [...]
>
>> +static void update_tasks_root_domain(struct cpuset *cs)
>> +{
>> + struct css_task_iter it;
>> + struct task_struct *task;
>> +
>> + css_task_iter_start(&cs->css, 0, &it);
>> +
>> + while ((task = css_task_iter_next(&it)))
>> + dl_add_task_root_domain(task);
>> +
>> + css_task_iter_end(&it);
>> +}
>> +
>> +/*
>> + * Called with cpuset_mutex held (rebuild_sched_domains())
>> + * Called with hotplug lock held (rebuild_sched_domains_locked())
>> + * Called with sched_domains_mutex held (partition_and_rebuild_domains())
>> + */
>> +static void rebuild_root_domains(void)
>> +{
>> + struct cpuset *cs = NULL;
>> + struct cgroup_subsys_state *pos_css;
>> +
>> + rcu_read_lock();
>> +
>> + /*
>> + * Clear default root domain DL accounting, it will be computed again
>> + * if a task belongs to it.
>> + */
>> + dl_clear_root_domain(&def_root_domain);
>
> Can't a __sched_setscheduler sneak in at this point, set a task to
> DEADLINE, add its bandwidth to the rd...

Let me think about that one for a bit.

Thanks for the review,
Mathieu

>
>> +
>> + cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
>> +
>> + if (cpumask_empty(cs->effective_cpus)) {
>> + pos_css = css_rightmost_descendant(pos_css);
>> + continue;
>> + }
>> +
>> + css_get(&cs->css);
>> +
>> + rcu_read_unlock();
>> +
>> + update_tasks_root_domain(cs);
>
> ... and this adds it again?
>
>> +
>> + rcu_read_lock();
>> + css_put(&cs->css);
>> + }
>> + rcu_read_unlock();
>> +}
>
> Best,
>
> - Juri

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