lkml.org 
[lkml]   [2008]   [Nov]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 04/13] dmaengine: centralize channel allocation, introduce dma_find_channel
Date
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

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---

crypto/async_tx/async_tx.c | 146 +---------------------------------------
drivers/dma/dmaengine.c | 159 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/dmaengine.h | 3 +
3 files changed, 166 insertions(+), 142 deletions(-)

diff --git a/crypto/async_tx/async_tx.c b/crypto/async_tx/async_tx.c
index 43fe4cb..b88bb1f 100644
--- a/crypto/async_tx/async_tx.c
+++ b/crypto/async_tx/async_tx.c
@@ -38,25 +38,10 @@ static struct dma_client async_tx_dma = {
};

/**
- * 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
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index df37073..c3e6fbb 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -284,6 +284,162 @@ static void dma_chan_release(struct dma_chan *chan)
}

/**
+ * 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/opertion
+ */
+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 = 1;
+ 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
+ */
+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 opertaion isolation (avoid
+ * multi-tasking channels) in the uniprocessor 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
*/
static void dma_clients_notify_available(void)
@@ -457,6 +613,7 @@ 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();
@@ -498,6 +655,7 @@ 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) {
@@ -743,3 +901,4 @@ static int __init dma_bus_init(void)
}
subsys_initcall(dma_bus_init);

+
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index d18d37d..b466f02 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -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 --- */



\
 
 \ /
  Last update: 2008-11-14 22:39    [W:0.451 / U:0.340 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site