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net: buf: Switch from k_fifo to k_lifo for free buffers

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Using a LIFO instead of a FIFO has the potential benefit that more
recently in-use buffers may be "cache-hot" and therefore accessed
faster than least recently used (which is what we get with a FIFO).

Change-Id: I59bb083ca2e00d0d404406540f7db216742a27cf
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
This commit is contained in:
Johan Hedberg 2016-12-14 08:24:19 +02:00
commit 692771fbe9
3 changed files with 12 additions and 13 deletions
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5
doc/subsystems/networking/buffers.rst
View file

@ -39,9 +39,8 @@ buffers may also contain protocol-specific context, known as user data.
Both the maximum data and user data capacity of the buffers is
compile-time defined when declaring the buffer pool.
Since the free buffers are managed with the help of a k_fifo it means
the buffers have native support for being passed through other FIFOs
as well. This is a very practical feature when the buffers need to be
The buffers have native support for being passed through k_fifo kernel
objects. This is a very practical feature when the buffers need to be
passed from one thread to another. However, since a net_buf may have a
fragment chain attached to it, instead of using the :c:func:`k_fifo_put`
and :c:func:`k_fifo_get` APIs, special :c:func:`net_buf_put` and

8
include/net/buf.h
View file

@ -434,8 +434,8 @@ struct net_buf {
};
struct net_buf_pool {
/** FIFO to place the buffer into when free */
struct k_fifo free;
/** LIFO to place the buffer into when free */
struct k_lifo free;
/** Number of buffers in pool */
const uint16_t buf_count;
@ -459,7 +459,7 @@ struct net_buf_pool {
#define NET_BUF_POOL_INITIALIZER(_pool, _bufs, _count, _size, _ud_size, \
_destroy) \
{ \
.free = K_FIFO_INITIALIZER(_pool.free), \
.free = K_LIFO_INITIALIZER(_pool.free), \
.__bufs = (struct net_buf *)_bufs, \
.buf_count = _count, \
.uninit_count = _count, \
@ -553,7 +553,7 @@ struct net_buf *net_buf_get(struct k_fifo *fifo, int32_t timeout);
*/
static inline void net_buf_destroy(struct net_buf *buf)
{
k_fifo_put(&buf->pool->free, buf);
k_lifo_put(&buf->pool->free, buf);
}
/**

12
subsys/net/buf.c
View file

@ -95,10 +95,10 @@ struct net_buf *net_buf_alloc(struct net_buf_pool *pool, int32_t timeout)
/* If this is not the first access to the pool, we can
* be opportunistic and try to fetch a previously used
* buffer from the FIFO with K_NO_WAIT.
* buffer from the LIFO with K_NO_WAIT.
*/
if (pool->uninit_count < pool->buf_count) {
buf = k_fifo_get(&pool->free, K_NO_WAIT);
buf = k_lifo_get(&pool->free, K_NO_WAIT);
if (buf) {
irq_unlock(key);
goto success;
@ -116,17 +116,17 @@ struct net_buf *net_buf_alloc(struct net_buf_pool *pool, int32_t timeout)
#if defined(CONFIG_NET_BUF_DEBUG)
if (timeout == K_FOREVER) {
buf = k_fifo_get(&pool->free, K_NO_WAIT);
buf = k_lifo_get(&pool->free, K_NO_WAIT);
if (!buf) {
NET_BUF_WARN("%s():%d: Pool %p low on buffers.",
func, line, pool);
buf = k_fifo_get(&pool->free, timeout);
buf = k_lifo_get(&pool->free, timeout);
}
} else {
buf = k_fifo_get(&pool->free, timeout);
buf = k_lifo_get(&pool->free, timeout);
}
#else
buf = k_fifo_get(&pool->free, timeout);
buf = k_lifo_get(&pool->free, timeout);
#endif
if (!buf) {
NET_BUF_ERR("%s():%d: Failed to get free buffer", func, line);