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rcu-tasks: Introduce ->percpu_enqueue_shift for dynamic queue selection
This commit introduces a ->percpu_enqueue_shift field to the rcu_tasks structure, and uses it to shift down the CPU number in order to select a rcu_tasks_percpu structure. This field is currently set to a sufficiently large shift count to always select the CPU-0 instance of the rcu_tasks_percpu structure, and later commits will adjust this. Reported-by: Martin Lau <kafai@fb.com> Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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@ -52,6 +52,7 @@ struct rcu_tasks_percpu {
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* @postgp_func: This flavor's post-grace-period function (optional).
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* @call_func: This flavor's call_rcu()-equivalent function.
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* @rtpcpu: This flavor's rcu_tasks_percpu structure.
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* @percpu_enqueue_shift: Shift down CPU ID this much when enqueuing callbacks.
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* @name: This flavor's textual name.
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* @kname: This flavor's kthread name.
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*/
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@ -75,6 +76,7 @@ struct rcu_tasks {
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postgp_func_t postgp_func;
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call_rcu_func_t call_func;
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struct rcu_tasks_percpu __percpu *rtpcpu;
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int percpu_enqueue_shift;
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char *name;
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char *kname;
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};
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@ -91,6 +93,7 @@ static struct rcu_tasks rt_name = \
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.call_func = call, \
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.rtpcpu = &rt_name ## __percpu, \
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.name = n, \
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.percpu_enqueue_shift = ilog2(CONFIG_NR_CPUS), \
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.kname = #rt_name, \
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}
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@ -169,6 +172,7 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
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unsigned long flags;
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raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);
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rtp->percpu_enqueue_shift = ilog2(nr_cpu_ids);
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for_each_possible_cpu(cpu) {
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struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
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@ -195,7 +199,8 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
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rhp->next = NULL;
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rhp->func = func;
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local_irq_save(flags);
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rtpcp = per_cpu_ptr(rtp->rtpcpu, 0 /* smp_processor_id() */);
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rtpcp = per_cpu_ptr(rtp->rtpcpu,
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smp_processor_id() >> READ_ONCE(rtp->percpu_enqueue_shift));
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raw_spin_lock(&rtpcp->cbs_pcpu_lock);
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if (!rtpcp->cbs_tail) {
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raw_spin_unlock(&rtpcp->cbs_pcpu_lock); // irqs remain disabled.
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