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

Kamezawa Hiroyuki
2014-12-15T02:56:18Z

(2014/12/15 11:48), Lai Jiangshan wrote:
> 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.
>

I'm sorry that I can't understand what this patch breaks.
Do you mean it's better to work with broken wq_numa_possible_cpumask ?

I guess removing wq_numa_possible_mask entirely may be the best way
byusing online_mask of the node.

Thanks,
-Kame