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

    > + 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);



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