Re: [PATCH 4/4] workqueue: handle change in cpu-node relationship.

Lai Jiangshan
2014-12-15T02:44:31Z

On 12/15/2014 10:20 AM, Kamezawa Hiroyuki wrote:
> (2014/12/15 11:12), Lai Jiangshan wrote:
>> On 12/14/2014 12:38 AM, Kamezawa Hiroyuki wrote:
>>> Although workqueue detects relationship between cpu<->node at boot,
>>> it is finally determined in cpu_up().
>>> This patch tries to update pool->node using online status of cpus.
>>>
>>> 1. When a node goes down, clear per-cpu pool's node attr.
>>> 2. When a cpu comes up, update per-cpu pool's node attr.
>>> 3. When a cpu comes up, update possinle node cpumask workqueue is using for sched.
>>> 4. Detect the best node for unbound pool's cpumask using the latest info.
>>>
>>> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>>> ---
>>> kernel/workqueue.c | 67 ++++++++++++++++++++++++++++++++++++++++++------------
>>> 1 file changed, 53 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
>>> index 07b4eb5..259b3ba 100644
>>> --- a/kernel/workqueue.c
>>> +++ b/kernel/workqueue.c
>>> @@ -266,7 +266,8 @@ struct workqueue_struct {
>>> static struct kmem_cache *pwq_cache;
>>>
>>> static cpumask_var_t *wq_numa_possible_cpumask;
>>> - /* possible CPUs of each node */
>>> + /* possible CPUs of each node initialized with possible info at boot.
>>> + but modified at cpu hotplug to be adjusted to real info. */
>>>
>>> static bool wq_disable_numa;
>>> module_param_named(disable_numa, wq_disable_numa, bool, 0444);
>>> @@ -3449,6 +3450,31 @@ static void put_unbound_pool(struct worker_pool *pool)
>>> call_rcu_sched(&pool->rcu, rcu_free_pool);
>>> }
>>>
>>> +/*
>>> + * detect best node for given cpumask.
>>> + */
>>> +static int pool_detect_best_node(const struct cpumask *cpumask)
>>> +{
>>> + int node, best, match, selected;
>>> + static struct cpumask andmask; /* we're under mutex */
>>> +
>>> + /* Is any node okay ? */
>>> + if (!wq_numa_enabled ||
>>> + cpumask_subset(cpu_online_mask, cpumask))
>>> + return NUMA_NO_NODE;
>>> + best = 0;
>>> + selected = NUMA_NO_NODE;
>>> + /* select a node which contains the most cpu of cpumask */
>>> + for_each_node_state(node, N_ONLINE) {
>>> + cpumask_and(&andmask, cpumask, cpumask_of_node(node));
>>> + match = cpumask_weight(&andmask);
>>> + if (match > best)
>>> + selected = node;
>>> + }
>>> + return selected;
>>> +}
>>> +
>>> +
>>> /**
>>> * get_unbound_pool - get a worker_pool with the specified attributes
>>> * @attrs: the attributes of the worker_pool to get
>>> @@ -3467,7 +3493,6 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
>>> {
>>> u32 hash = wqattrs_hash(attrs);
>>> struct worker_pool *pool;
>>> - int node;
>>>
>>> lockdep_assert_held(&wq_pool_mutex);
>>>
>>> @@ -3492,17 +3517,7 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
>>> * 'struct workqueue_attrs' comments for detail.
>>> */
>>> pool->attrs->no_numa = false;
>>> -
>>> - /* if cpumask is contained inside a NUMA node, we belong to that node */
>>> - if (wq_numa_enabled) {
>>> - for_each_node(node) {
>>> - if (cpumask_subset(pool->attrs->cpumask,
>>> - wq_numa_possible_cpumask[node])) {
>>> - pool->node = node;
>>> - break;
>>> - }
>>> - }
>>> - }
>>> + pool->node = pool_detect_best_node(pool->attrs->cpumask);
>>>
>>> if (worker_pool_assign_id(pool) < 0)
>>> goto fail;
>>> @@ -4567,7 +4582,7 @@ static int workqueue_cpu_up_callback(struct notifier_block *nfb,
>>> int cpu = (unsigned long)hcpu;
>>> struct worker_pool *pool;
>>> struct workqueue_struct *wq;
>>> - int pi;
>>> + int pi, node;
>>>
>>> switch (action & ~CPU_TASKS_FROZEN) {
>>> case CPU_UP_PREPARE:
>>> @@ -4583,6 +4598,16 @@ static int workqueue_cpu_up_callback(struct notifier_block *nfb,
>>> case CPU_ONLINE:
>>> mutex_lock(&wq_pool_mutex);
>>>
>>> + /* now cpu <-> node info is established, update the info. */
>>> + if (!wq_disable_numa) {
>>
>>
>>
>>> + for_each_node_state(node, N_POSSIBLE)
>>> + cpumask_clear_cpu(cpu,
>>> + wq_numa_possible_cpumask[node]);
>>
>> The wq code try to reuse the origin pwqs/pools when the node still have cpu online.
>> these 3 lines of code will cause the origin pwqs/pools be on the road of dying, and
>> create a new set of pwqs/pools.
>
> because the result of wq_calc_node_cpumask() changes ?

Yes.

> Do you mean some comment should be added here ? or explaination for your reply for [3/4] ?

this fix [4/4] breaks the original design.

>
> Thanks,
> -Kame
>
>
>
>
>
>>
>>> + node = cpu_to_node(cpu);
>>> + cpumask_set_cpu(cpu, wq_numa_possible_cpumask[node]);
>>> + }
>>> + for_each_cpu_worker_pool(pool, cpu)
>>> + pool->node = cpu_to_node(cpu);
>>> for_each_pool(pool, pi) {
>>> mutex_lock(&pool->attach_mutex);
>>>
>>> @@ -4951,7 +4976,21 @@ void workqueue_register_numanode(int nid)
>>> void workqueue_unregister_numanode(int nid)
>>> {
>>> struct workqueue_struct *wq;
>>> + const struct cpumask *nodecpumask;
>>> + struct worker_pool *pool;
>>> + int cpu;
>>>
>>> + /* at this point, cpu-to-node relationship is not lost */
>>> + nodecpumask = cpumask_of_node(nid);
>>> + for_each_cpu(cpu, nodecpumask) {
>>> + /*
>>> + * pool is allcated at boot and assumed to be persistent,
>>> + * we cannot free this.
>>> + * Update to be NUMA_NO_NODE. This will be fixed at ONLINE
>>> + */
>>> + for_each_cpu_worker_pool(pool, cpu)
>>> + pool->node = NUMA_NO_NODE;
>>> + }
>>> mutex_lock(&wq_pool_mutex);
>>> list_for_each_entry(wq, &workqueues, list)
>>> wq_release_unbound_numa(wq, nid);
>>
>
>
> .
>