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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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
This commit is contained in:
Dan Williams 2009-01-06 11:38:14 -07:00
parent 6f49a57aa5
commit bec085134e
3 changed files with 174 additions and 143 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

146
crypto/async_tx/async_tx.c
View File

@ -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);
}
@ -308,16 +177,9 @@ __async_tx_find_channel(struct dma_async_tx_descriptor *depend_tx,
{
/* see if we can keep the chain on one channel */
if (depend_tx &&
dma_has_cap(tx_type, depend_tx->chan->device->cap_mask))
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

168
drivers/dma/dmaengine.c
View File

@ -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);

3
include/linux/dmaengine.h
View File

@ -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 --- */