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padata: Add some code comments

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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 2010-05-19 13:44:27 +10:00 committed by Herbert Xu
parent 2b73b07ab8
commit 0198ffd135
2 changed files with 110 additions and 11 deletions
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53
include/linux/padata.h
View File

@ -26,6 +26,17 @@
#include <linux/list.h>
#include <linux/timer.h>
/**
* struct padata_priv - Embedded to the users data structure.
*
* @list: List entry, to attach to the padata lists.
* @pd: Pointer to the internal control structure.
* @cb_cpu: Callback cpu for serializatioon.
* @seq_nr: Sequence number of the parallelized data object.
* @info: Used to pass information from the parallel to the serial function.
* @parallel: Parallel execution function.
* @serial: Serial complete function.
*/
struct padata_priv {
struct list_head list;
struct parallel_data *pd;
@ -36,11 +47,29 @@ struct padata_priv {
void (*serial)(struct padata_priv *padata);
};
/**
* struct padata_list
*
* @list: List head.
* @lock: List lock.
*/
struct padata_list {
struct list_head list;
spinlock_t lock;
};
/**
* struct padata_queue - The percpu padata queues.
*
* @parallel: List to wait for parallelization.
* @reorder: List to wait for reordering after parallel processing.
* @serial: List to wait for serialization after reordering.
* @pwork: work struct for parallelization.
* @swork: work struct for serialization.
* @pd: Backpointer to the internal control structure.
* @num_obj: Number of objects that are processed by this cpu.
* @cpu_index: Index of the cpu.
*/
struct padata_queue {
struct padata_list parallel;
struct padata_list reorder;
@ -52,6 +81,20 @@ struct padata_queue {
int cpu_index;
};
/**
* struct parallel_data - Internal control structure, covers everything
* that depends on the cpumask in use.
*
* @pinst: padata instance.
* @queue: percpu padata queues.
* @seq_nr: The sequence number that will be attached to the next object.
* @reorder_objects: Number of objects waiting in the reorder queues.
* @refcnt: Number of objects holding a reference on this parallel_data.
* @max_seq_nr: Maximal used sequence number.
* @cpumask: cpumask in use.
* @lock: Reorder lock.
* @timer: Reorder timer.
*/
struct parallel_data {
struct padata_instance *pinst;
struct padata_queue *queue;
@ -64,6 +107,16 @@ struct parallel_data {
struct timer_list timer;
};
/**
* struct padata_instance - The overall control structure.
*
* @cpu_notifier: cpu hotplug notifier.
* @wq: The workqueue in use.
* @pd: The internal control structure.
* @cpumask: User supplied cpumask.
* @lock: padata instance lock.
* @flags: padata flags.
*/
struct padata_instance {
struct notifier_block cpu_notifier;
struct workqueue_struct *wq;

68
kernel/padata.c
View File

@ -88,7 +88,7 @@ static void padata_parallel_worker(struct work_struct *work)
local_bh_enable();
}
/*
/**
* padata_do_parallel - padata parallelization function
*
* @pinst: padata instance
@ -152,6 +152,23 @@ out:
}
EXPORT_SYMBOL(padata_do_parallel);
/*
* padata_get_next - Get the next object that needs serialization.
*
* Return values are:
*
* A pointer to the control struct of the next object that needs
* serialization, if present in one of the percpu reorder queues.
*
* NULL, if all percpu reorder queues are empty.
*
* -EINPROGRESS, if the next object that needs serialization will
* be parallel processed by another cpu and is not yet present in
* the cpu's reorder queue.
*
* -ENODATA, if this cpu has to do the parallel processing for
* the next object.
*/
static struct padata_priv *padata_get_next(struct parallel_data *pd)
{
int cpu, num_cpus, empty, calc_seq_nr;
@ -173,7 +190,7 @@ static struct padata_priv *padata_get_next(struct parallel_data *pd)
/*
* Calculate the seq_nr of the object that should be
* next in this queue.
* next in this reorder queue.
*/
overrun = 0;
calc_seq_nr = (atomic_read(&queue->num_obj) * num_cpus)
@ -248,15 +265,36 @@ static void padata_reorder(struct parallel_data *pd)
struct padata_queue *queue;
struct padata_instance *pinst = pd->pinst;
/*
* We need to ensure that only one cpu can work on dequeueing of
* the reorder queue the time. Calculating in which percpu reorder
* queue the next object will arrive takes some time. A spinlock
* would be highly contended. Also it is not clear in which order
* the objects arrive to the reorder queues. So a cpu could wait to
* get the lock just to notice that there is nothing to do at the
* moment. Therefore we use a trylock and let the holder of the lock
* care for all the objects enqueued during the holdtime of the lock.
*/
if (!spin_trylock_bh(&pd->lock))
return;
while (1) {
padata = padata_get_next(pd);
/*
* All reorder queues are empty, or the next object that needs
* serialization is parallel processed by another cpu and is
* still on it's way to the cpu's reorder queue, nothing to
* do for now.
*/
if (!padata || PTR_ERR(padata) == -EINPROGRESS)
break;
/*
* This cpu has to do the parallel processing of the next
* object. It's waiting in the cpu's parallelization queue,
* so exit imediately.
*/
if (PTR_ERR(padata) == -ENODATA) {
del_timer(&pd->timer);
spin_unlock_bh(&pd->lock);
@ -274,6 +312,11 @@ static void padata_reorder(struct parallel_data *pd)
spin_unlock_bh(&pd->lock);
/*
* The next object that needs serialization might have arrived to
* the reorder queues in the meantime, we will be called again
* from the timer function if noone else cares for it.
*/
if (atomic_read(&pd->reorder_objects)
&& !(pinst->flags & PADATA_RESET))
mod_timer(&pd->timer, jiffies + HZ);
@ -318,7 +361,7 @@ static void padata_serial_worker(struct work_struct *work)
local_bh_enable();
}
/*
/**
* padata_do_serial - padata serialization function
*
* @padata: object to be serialized.
@ -348,6 +391,7 @@ void padata_do_serial(struct padata_priv *padata)
}
EXPORT_SYMBOL(padata_do_serial);
/* Allocate and initialize the internal cpumask dependend resources. */
static struct parallel_data *padata_alloc_pd(struct padata_instance *pinst,
const struct cpumask *cpumask)
{
@ -417,6 +461,7 @@ static void padata_free_pd(struct parallel_data *pd)
kfree(pd);
}
/* Flush all objects out of the padata queues. */
static void padata_flush_queues(struct parallel_data *pd)
{
int cpu;
@ -440,6 +485,7 @@ static void padata_flush_queues(struct parallel_data *pd)
BUG_ON(atomic_read(&pd->refcnt) != 0);
}
/* Replace the internal control stucture with a new one. */
static void padata_replace(struct padata_instance *pinst,
struct parallel_data *pd_new)
{
@ -457,7 +503,7 @@ static void padata_replace(struct padata_instance *pinst,
pinst->flags &= ~PADATA_RESET;
}
/*
/**
* padata_set_cpumask - set the cpumask that padata should use
*
* @pinst: padata instance
@ -507,7 +553,7 @@ static int __padata_add_cpu(struct padata_instance *pinst, int cpu)
return 0;
}
/*
/**
* padata_add_cpu - add a cpu to the padata cpumask
*
* @pinst: padata instance
@ -545,7 +591,7 @@ static int __padata_remove_cpu(struct padata_instance *pinst, int cpu)
return 0;
}
/*
/**
* padata_remove_cpu - remove a cpu from the padata cpumask
*
* @pinst: padata instance
@ -568,7 +614,7 @@ int padata_remove_cpu(struct padata_instance *pinst, int cpu)
}
EXPORT_SYMBOL(padata_remove_cpu);
/*
/**
* padata_start - start the parallel processing
*
* @pinst: padata instance to start
@ -581,7 +627,7 @@ void padata_start(struct padata_instance *pinst)
}
EXPORT_SYMBOL(padata_start);
/*
/**
* padata_stop - stop the parallel processing
*
* @pinst: padata instance to stop
@ -648,7 +694,7 @@ static int padata_cpu_callback(struct notifier_block *nfb,
}
#endif
/*
/**
* padata_alloc - allocate and initialize a padata instance
*
* @cpumask: cpumask that padata uses for parallelization
@ -703,10 +749,10 @@ err:
}
EXPORT_SYMBOL(padata_alloc);
/*
/**
* padata_free - free a padata instance
*
* @ padata_inst: padata instance to free
* @padata_inst: padata instance to free
*/
void padata_free(struct padata_instance *pinst)
{