padata: Add some code comments
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Steffen Klassert
Herbert Xu
parent
2b73b07ab8
commit
0198ffd135
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@ -26,6 +26,17 @@
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#include <linux/list.h>
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#include <linux/timer.h>
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/**
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* struct padata_priv - Embedded to the users data structure.
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*
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* @list: List entry, to attach to the padata lists.
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* @pd: Pointer to the internal control structure.
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* @cb_cpu: Callback cpu for serializatioon.
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* @seq_nr: Sequence number of the parallelized data object.
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* @info: Used to pass information from the parallel to the serial function.
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* @parallel: Parallel execution function.
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* @serial: Serial complete function.
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*/
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struct padata_priv {
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struct list_head list;
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struct parallel_data *pd;
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@ -36,11 +47,29 @@ struct padata_priv {
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void (*serial)(struct padata_priv *padata);
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};
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/**
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* struct padata_list
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*
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* @list: List head.
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* @lock: List lock.
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*/
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struct padata_list {
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struct list_head list;
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spinlock_t lock;
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};
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/**
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* struct padata_queue - The percpu padata queues.
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*
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* @parallel: List to wait for parallelization.
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* @reorder: List to wait for reordering after parallel processing.
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* @serial: List to wait for serialization after reordering.
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* @pwork: work struct for parallelization.
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* @swork: work struct for serialization.
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* @pd: Backpointer to the internal control structure.
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* @num_obj: Number of objects that are processed by this cpu.
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* @cpu_index: Index of the cpu.
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*/
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struct padata_queue {
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struct padata_list parallel;
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struct padata_list reorder;
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@ -52,6 +81,20 @@ struct padata_queue {
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int cpu_index;
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};
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/**
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* struct parallel_data - Internal control structure, covers everything
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* that depends on the cpumask in use.
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*
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* @pinst: padata instance.
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* @queue: percpu padata queues.
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* @seq_nr: The sequence number that will be attached to the next object.
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* @reorder_objects: Number of objects waiting in the reorder queues.
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* @refcnt: Number of objects holding a reference on this parallel_data.
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* @max_seq_nr: Maximal used sequence number.
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* @cpumask: cpumask in use.
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* @lock: Reorder lock.
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* @timer: Reorder timer.
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*/
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struct parallel_data {
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struct padata_instance *pinst;
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struct padata_queue *queue;
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@ -64,6 +107,16 @@ struct parallel_data {
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struct timer_list timer;
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};
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/**
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* struct padata_instance - The overall control structure.
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*
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* @cpu_notifier: cpu hotplug notifier.
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* @wq: The workqueue in use.
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* @pd: The internal control structure.
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* @cpumask: User supplied cpumask.
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* @lock: padata instance lock.
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* @flags: padata flags.
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*/
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struct padata_instance {
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struct notifier_block cpu_notifier;
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struct workqueue_struct *wq;
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@ -88,7 +88,7 @@ static void padata_parallel_worker(struct work_struct *work)
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local_bh_enable();
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}
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/*
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/**
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* padata_do_parallel - padata parallelization function
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*
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* @pinst: padata instance
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@ -152,6 +152,23 @@ out:
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}
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EXPORT_SYMBOL(padata_do_parallel);
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/*
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* padata_get_next - Get the next object that needs serialization.
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*
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* Return values are:
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*
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* A pointer to the control struct of the next object that needs
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* serialization, if present in one of the percpu reorder queues.
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*
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* NULL, if all percpu reorder queues are empty.
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*
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* -EINPROGRESS, if the next object that needs serialization will
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* be parallel processed by another cpu and is not yet present in
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* the cpu's reorder queue.
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*
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* -ENODATA, if this cpu has to do the parallel processing for
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* the next object.
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*/
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static struct padata_priv *padata_get_next(struct parallel_data *pd)
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{
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int cpu, num_cpus, empty, calc_seq_nr;
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@ -173,7 +190,7 @@ static struct padata_priv *padata_get_next(struct parallel_data *pd)
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/*
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* Calculate the seq_nr of the object that should be
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* next in this queue.
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* next in this reorder queue.
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*/
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overrun = 0;
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calc_seq_nr = (atomic_read(&queue->num_obj) * num_cpus)
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@ -248,15 +265,36 @@ static void padata_reorder(struct parallel_data *pd)
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struct padata_queue *queue;
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struct padata_instance *pinst = pd->pinst;
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/*
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* We need to ensure that only one cpu can work on dequeueing of
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* the reorder queue the time. Calculating in which percpu reorder
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* queue the next object will arrive takes some time. A spinlock
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* would be highly contended. Also it is not clear in which order
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* the objects arrive to the reorder queues. So a cpu could wait to
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* get the lock just to notice that there is nothing to do at the
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* moment. Therefore we use a trylock and let the holder of the lock
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* care for all the objects enqueued during the holdtime of the lock.
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*/
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if (!spin_trylock_bh(&pd->lock))
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return;
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while (1) {
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padata = padata_get_next(pd);
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/*
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* All reorder queues are empty, or the next object that needs
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* serialization is parallel processed by another cpu and is
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* still on it's way to the cpu's reorder queue, nothing to
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* do for now.
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*/
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if (!padata || PTR_ERR(padata) == -EINPROGRESS)
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break;
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/*
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* This cpu has to do the parallel processing of the next
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* object. It's waiting in the cpu's parallelization queue,
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* so exit imediately.
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*/
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if (PTR_ERR(padata) == -ENODATA) {
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del_timer(&pd->timer);
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spin_unlock_bh(&pd->lock);
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@ -274,6 +312,11 @@ static void padata_reorder(struct parallel_data *pd)
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spin_unlock_bh(&pd->lock);
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/*
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* The next object that needs serialization might have arrived to
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* the reorder queues in the meantime, we will be called again
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* from the timer function if noone else cares for it.
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*/
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if (atomic_read(&pd->reorder_objects)
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&& !(pinst->flags & PADATA_RESET))
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mod_timer(&pd->timer, jiffies + HZ);
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@ -318,7 +361,7 @@ static void padata_serial_worker(struct work_struct *work)
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local_bh_enable();
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}
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/*
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/**
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* padata_do_serial - padata serialization function
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*
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* @padata: object to be serialized.
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@ -348,6 +391,7 @@ void padata_do_serial(struct padata_priv *padata)
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}
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EXPORT_SYMBOL(padata_do_serial);
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/* Allocate and initialize the internal cpumask dependend resources. */
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static struct parallel_data *padata_alloc_pd(struct padata_instance *pinst,
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const struct cpumask *cpumask)
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{
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@ -417,6 +461,7 @@ static void padata_free_pd(struct parallel_data *pd)
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kfree(pd);
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}
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/* Flush all objects out of the padata queues. */
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static void padata_flush_queues(struct parallel_data *pd)
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{
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int cpu;
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@ -440,6 +485,7 @@ static void padata_flush_queues(struct parallel_data *pd)
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BUG_ON(atomic_read(&pd->refcnt) != 0);
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}
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/* Replace the internal control stucture with a new one. */
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static void padata_replace(struct padata_instance *pinst,
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struct parallel_data *pd_new)
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{
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@ -457,7 +503,7 @@ static void padata_replace(struct padata_instance *pinst,
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pinst->flags &= ~PADATA_RESET;
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}
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/*
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/**
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* padata_set_cpumask - set the cpumask that padata should use
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*
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* @pinst: padata instance
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@ -507,7 +553,7 @@ static int __padata_add_cpu(struct padata_instance *pinst, int cpu)
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return 0;
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}
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/*
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/**
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* padata_add_cpu - add a cpu to the padata cpumask
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*
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* @pinst: padata instance
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@ -545,7 +591,7 @@ static int __padata_remove_cpu(struct padata_instance *pinst, int cpu)
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return 0;
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}
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/*
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/**
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* padata_remove_cpu - remove a cpu from the padata cpumask
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*
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* @pinst: padata instance
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@ -568,7 +614,7 @@ int padata_remove_cpu(struct padata_instance *pinst, int cpu)
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}
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EXPORT_SYMBOL(padata_remove_cpu);
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/*
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/**
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* padata_start - start the parallel processing
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*
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* @pinst: padata instance to start
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@ -581,7 +627,7 @@ void padata_start(struct padata_instance *pinst)
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}
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EXPORT_SYMBOL(padata_start);
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/*
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/**
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* padata_stop - stop the parallel processing
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*
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* @pinst: padata instance to stop
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@ -648,7 +694,7 @@ static int padata_cpu_callback(struct notifier_block *nfb,
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}
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#endif
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/*
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/**
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* padata_alloc - allocate and initialize a padata instance
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*
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* @cpumask: cpumask that padata uses for parallelization
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@ -703,10 +749,10 @@ err:
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}
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EXPORT_SYMBOL(padata_alloc);
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/*
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/**
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* padata_free - free a padata instance
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*
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* @ padata_inst: padata instance to free
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* @padata_inst: padata instance to free
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*/
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void padata_free(struct padata_instance *pinst)
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{
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