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

[Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

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

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);
>