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

[Kamezawa Hiroyuki]

(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@xxxxxxxxxxxxxx>
> > > > ---
> > > >    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




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