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Commit bec08513 authored by Dan Williams's avatar Dan Williams
Browse files

dmaengine: centralize channel allocation, introduce dma_find_channel 



Allowing multiple clients to each define their own channel allocation
scheme quickly leads to a pathological situation.  For memory-to-memory
offload all clients can share a central allocator.

This simply moves the existing async_tx allocator to dmaengine with
minimal fixups:
* async_tx.c:get_chan_ref_by_cap --> dmaengine.c:nth_chan
* async_tx.c:async_tx_rebalance --> dmaengine.c:dma_channel_rebalance
* split out common code from async_tx.c:__async_tx_find_channel -->
  dma_find_channel

Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
parent 6f49a57a

crypto/async_tx/async_tx.c

+4 −142
Original line number Diff line number Diff line
@@ -37,26 +37,11 @@ static struct dma_client async_tx_dma = { 
	/* .cap_mask == 0 defaults to all channels */

};



/**

 * dma_cap_mask_all - enable iteration over all operation types

 */

static dma_cap_mask_t dma_cap_mask_all;



/**

 * chan_ref_percpu - tracks channel allocations per core/opertion

 */

struct chan_ref_percpu {

	struct dma_chan_ref *ref;

};



static int channel_table_initialized;

static struct chan_ref_percpu *channel_table[DMA_TX_TYPE_END];



/**

 * async_tx_lock - protect modification of async_tx_master_list and serialize

 *	rebalance operations

 */

static spinlock_t async_tx_lock;

static DEFINE_SPINLOCK(async_tx_lock);



static LIST_HEAD(async_tx_master_list);
@@ -89,85 +74,6 @@ init_dma_chan_ref(struct dma_chan_ref *ref, struct dma_chan *chan) 
	atomic_set(&ref->count, 0);

}



/**

 * get_chan_ref_by_cap - returns the nth channel of the given capability

 * 	defaults to returning the channel with the desired capability and the

 * 	lowest reference count if the index can not be satisfied

 * @cap: capability to match

 * @index: nth channel desired, passing -1 has the effect of forcing the

 *  default return value

 */

static struct dma_chan_ref *

get_chan_ref_by_cap(enum dma_transaction_type cap, int index)

{

	struct dma_chan_ref *ret_ref = NULL, *min_ref = NULL, *ref;



	rcu_read_lock();

	list_for_each_entry_rcu(ref, &async_tx_master_list, node)

		if (dma_has_cap(cap, ref->chan->device->cap_mask)) {

			if (!min_ref)

				min_ref = ref;

			else if (atomic_read(&ref->count) <

				atomic_read(&min_ref->count))

				min_ref = ref;



			if (index-- == 0) {

				ret_ref = ref;

				break;

			}

		}

	rcu_read_unlock();



	if (!ret_ref)

		ret_ref = min_ref;



	if (ret_ref)

		atomic_inc(&ret_ref->count);



	return ret_ref;

}



/**

 * async_tx_rebalance - redistribute the available channels, optimize

 * for cpu isolation in the SMP case, and opertaion isolation in the

 * uniprocessor case

 */

static void async_tx_rebalance(void)

{

	int cpu, cap, cpu_idx = 0;

	unsigned long flags;



	if (!channel_table_initialized)

		return;



	spin_lock_irqsave(&async_tx_lock, flags);



	/* undo the last distribution */

	for_each_dma_cap_mask(cap, dma_cap_mask_all)

		for_each_possible_cpu(cpu) {

			struct dma_chan_ref *ref =

				per_cpu_ptr(channel_table[cap], cpu)->ref;

			if (ref) {

				atomic_set(&ref->count, 0);

				per_cpu_ptr(channel_table[cap], cpu)->ref =

									NULL;

			}

		}



	for_each_dma_cap_mask(cap, dma_cap_mask_all)

		for_each_online_cpu(cpu) {

			struct dma_chan_ref *new;

			if (NR_CPUS > 1)

				new = get_chan_ref_by_cap(cap, cpu_idx++);

			else

				new = get_chan_ref_by_cap(cap, -1);



			per_cpu_ptr(channel_table[cap], cpu)->ref = new;

		}



	spin_unlock_irqrestore(&async_tx_lock, flags);

}



static enum dma_state_client

dma_channel_add_remove(struct dma_client *client,

	struct dma_chan *chan, enum dma_state state)
@@ -211,8 +117,6 @@ dma_channel_add_remove(struct dma_client *client, 
				" (-ENOMEM)\n");

			return 0;

		}



		async_tx_rebalance();

		break;

	case DMA_RESOURCE_REMOVED:

		found = 0;
@@ -233,8 +137,6 @@ dma_channel_add_remove(struct dma_client *client, 
			ack = DMA_ACK;

		else

			break;



		async_tx_rebalance();

		break;

	case DMA_RESOURCE_SUSPEND:

	case DMA_RESOURCE_RESUME:
@@ -248,51 +150,18 @@ dma_channel_add_remove(struct dma_client *client, 
	return ack;

}



static int __init

async_tx_init(void)

static int __init async_tx_init(void)

{

	enum dma_transaction_type cap;



	spin_lock_init(&async_tx_lock);

	bitmap_fill(dma_cap_mask_all.bits, DMA_TX_TYPE_END);



	/* an interrupt will never be an explicit operation type.

	 * clearing this bit prevents allocation to a slot in 'channel_table'

	 */

	clear_bit(DMA_INTERRUPT, dma_cap_mask_all.bits);



	for_each_dma_cap_mask(cap, dma_cap_mask_all) {

		channel_table[cap] = alloc_percpu(struct chan_ref_percpu);

		if (!channel_table[cap])

			goto err;

	}



	channel_table_initialized = 1;

	dma_async_client_register(&async_tx_dma);

	dma_async_client_chan_request(&async_tx_dma);



	printk(KERN_INFO "async_tx: api initialized (async)\n");



	return 0;

err:

	printk(KERN_ERR "async_tx: initialization failure\n");



	while (--cap >= 0)

		free_percpu(channel_table[cap]);



	return 1;

}



static void __exit async_tx_exit(void)

{

	enum dma_transaction_type cap;



	channel_table_initialized = 0;



	for_each_dma_cap_mask(cap, dma_cap_mask_all)

		if (channel_table[cap])

			free_percpu(channel_table[cap]);



	dma_async_client_unregister(&async_tx_dma);

}
@@ -310,14 +179,7 @@ __async_tx_find_channel(struct dma_async_tx_descriptor *depend_tx, 
	if (depend_tx &&

	    dma_has_cap(tx_type, depend_tx->chan->device->cap_mask))

		return depend_tx->chan;

	else if (likely(channel_table_initialized)) {

		struct dma_chan_ref *ref;

		int cpu = get_cpu();

		ref = per_cpu_ptr(channel_table[tx_type], cpu)->ref;

		put_cpu();

		return ref ? ref->chan : NULL;

	} else

		return NULL;

	return dma_find_channel(tx_type);

}

EXPORT_SYMBOL_GPL(__async_tx_find_channel);

#else

drivers/dma/dmaengine.c

+167 −1
Original line number Diff line number Diff line
@@ -294,6 +294,164 @@ static void dma_chan_release(struct dma_chan *chan) 
	call_rcu(&chan->rcu, dma_chan_free_rcu);

}



/**

 * dma_cap_mask_all - enable iteration over all operation types

 */

static dma_cap_mask_t dma_cap_mask_all;



/**

 * dma_chan_tbl_ent - tracks channel allocations per core/operation

 * @chan - associated channel for this entry

 */

struct dma_chan_tbl_ent {

	struct dma_chan *chan;

};



/**

 * channel_table - percpu lookup table for memory-to-memory offload providers

 */

static struct dma_chan_tbl_ent *channel_table[DMA_TX_TYPE_END];



static int __init dma_channel_table_init(void)

{

	enum dma_transaction_type cap;

	int err = 0;



	bitmap_fill(dma_cap_mask_all.bits, DMA_TX_TYPE_END);



	/* 'interrupt' and 'slave' are channel capabilities, but are not

	 * associated with an operation so they do not need an entry in the

	 * channel_table

	 */

	clear_bit(DMA_INTERRUPT, dma_cap_mask_all.bits);

	clear_bit(DMA_SLAVE, dma_cap_mask_all.bits);



	for_each_dma_cap_mask(cap, dma_cap_mask_all) {

		channel_table[cap] = alloc_percpu(struct dma_chan_tbl_ent);

		if (!channel_table[cap]) {

			err = -ENOMEM;

			break;

		}

	}



	if (err) {

		pr_err("dmaengine: initialization failure\n");

		for_each_dma_cap_mask(cap, dma_cap_mask_all)

			if (channel_table[cap])

				free_percpu(channel_table[cap]);

	}



	return err;

}

subsys_initcall(dma_channel_table_init);



/**

 * dma_find_channel - find a channel to carry out the operation

 * @tx_type: transaction type

 */

struct dma_chan *dma_find_channel(enum dma_transaction_type tx_type)

{

	struct dma_chan *chan;

	int cpu;



	WARN_ONCE(dmaengine_ref_count == 0,

		  "client called %s without a reference", __func__);



	cpu = get_cpu();

	chan = per_cpu_ptr(channel_table[tx_type], cpu)->chan;

	put_cpu();



	return chan;

}

EXPORT_SYMBOL(dma_find_channel);



/**

 * nth_chan - returns the nth channel of the given capability

 * @cap: capability to match

 * @n: nth channel desired

 *

 * Defaults to returning the channel with the desired capability and the

 * lowest reference count when 'n' cannot be satisfied.  Must be called

 * under dma_list_mutex.

 */

static struct dma_chan *nth_chan(enum dma_transaction_type cap, int n)

{

	struct dma_device *device;

	struct dma_chan *chan;

	struct dma_chan *ret = NULL;

	struct dma_chan *min = NULL;



	list_for_each_entry(device, &dma_device_list, global_node) {

		if (!dma_has_cap(cap, device->cap_mask))

			continue;

		list_for_each_entry(chan, &device->channels, device_node) {

			if (!chan->client_count)

				continue;

			if (!min)

				min = chan;

			else if (chan->table_count < min->table_count)

				min = chan;



			if (n-- == 0) {

				ret = chan;

				break; /* done */

			}

		}

		if (ret)

			break; /* done */

	}



	if (!ret)

		ret = min;



	if (ret)

		ret->table_count++;



	return ret;

}



/**

 * dma_channel_rebalance - redistribute the available channels

 *

 * Optimize for cpu isolation (each cpu gets a dedicated channel for an

 * operation type) in the SMP case,  and operation isolation (avoid

 * multi-tasking channels) in the non-SMP case.  Must be called under

 * dma_list_mutex.

 */

static void dma_channel_rebalance(void)

{

	struct dma_chan *chan;

	struct dma_device *device;

	int cpu;

	int cap;

	int n;



	/* undo the last distribution */

	for_each_dma_cap_mask(cap, dma_cap_mask_all)

		for_each_possible_cpu(cpu)

			per_cpu_ptr(channel_table[cap], cpu)->chan = NULL;



	list_for_each_entry(device, &dma_device_list, global_node)

		list_for_each_entry(chan, &device->channels, device_node)

			chan->table_count = 0;



	/* don't populate the channel_table if no clients are available */

	if (!dmaengine_ref_count)

		return;



	/* redistribute available channels */

	n = 0;

	for_each_dma_cap_mask(cap, dma_cap_mask_all)

		for_each_online_cpu(cpu) {

			if (num_possible_cpus() > 1)

				chan = nth_chan(cap, n++);

			else

				chan = nth_chan(cap, -1);



			per_cpu_ptr(channel_table[cap], cpu)->chan = chan;

		}

}



/**

 * dma_chans_notify_available - broadcast available channels to the clients

 */
@@ -339,7 +497,12 @@ void dma_async_client_register(struct dma_client *client) 
				       dev_name(&chan->dev), err);

		}





	/* if this is the first reference and there were channels

	 * waiting we need to rebalance to get those channels

	 * incorporated into the channel table

	 */

	if (dmaengine_ref_count == 1)

		dma_channel_rebalance();

	list_add_tail(&client->global_node, &dma_client_list);

	mutex_unlock(&dma_list_mutex);

}
@@ -473,6 +636,7 @@ int dma_async_device_register(struct dma_device *device) 
			}

		}

	list_add_tail(&device->global_node, &dma_device_list);

	dma_channel_rebalance();

	mutex_unlock(&dma_list_mutex);



	dma_clients_notify_available();
@@ -514,6 +678,7 @@ void dma_async_device_unregister(struct dma_device *device) 


	mutex_lock(&dma_list_mutex);

	list_del(&device->global_node);

	dma_channel_rebalance();

	mutex_unlock(&dma_list_mutex);



	list_for_each_entry(chan, &device->channels, device_node) {
@@ -768,3 +933,4 @@ static int __init dma_bus_init(void) 
}

subsys_initcall(dma_bus_init);

include/linux/dmaengine.h

+3 −0
Original line number Diff line number Diff line
@@ -182,6 +182,7 @@ struct dma_chan_percpu { 
 * @device_node: used to add this to the device chan list

 * @local: per-cpu pointer to a struct dma_chan_percpu

 * @client-count: how many clients are using this channel

 * @table_count: number of appearances in the mem-to-mem allocation table

 */

struct dma_chan {

	struct dma_device *device;
@@ -198,6 +199,7 @@ struct dma_chan { 
	struct list_head device_node;

	struct dma_chan_percpu *local;

	int client_count;

	int table_count;

};



#define to_dma_chan(p) container_of(p, struct dma_chan, dev)
@@ -468,6 +470,7 @@ static inline enum dma_status dma_wait_for_async_tx(struct dma_async_tx_descript 
int dma_async_device_register(struct dma_device *device);

void dma_async_device_unregister(struct dma_device *device);

void dma_run_dependencies(struct dma_async_tx_descriptor *tx);

struct dma_chan *dma_find_channel(enum dma_transaction_type tx_type);



/* --- Helper iov-locking functions --- */