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sfc: Simplify TSO header buffer allocation

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TSO header buffers contain a control structure immediately followed by
the packet headers, and are kept on a free list when not in use.  This
complicates buffer management and tends to result in cache read misses
when we recycle such buffers (particularly if DMA-coherent memory
requires caches to be disabled).

Replace the free list with a simple mapping by descriptor index.  We
know that there is always a payload descriptor between any two
descriptors with TSO header buffers, so we can allocate only one
such buffer for each two descriptors.

While we're at it, use a standard error code for allocation failure,
not -1.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
This commit is contained in:
Ben Hutchings
2012-05-17 18:40:54 +01:00
parent 14bf718fb9
commit f7251a9ce9
3 changed files with 116 additions and 222 deletions
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13
drivers/net/ethernet/sfc/net_driver.h
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@@ -94,7 +94,8 @@ struct efx_special_buffer {
* struct efx_tx_buffer - buffer state for a TX descriptor
* @skb: When @flags & %EFX_TX_BUF_SKB, the associated socket buffer to be
* freed when descriptor completes
* @tsoh: When @flags & %EFX_TX_BUF_TSOH, the associated TSO header structure.
* @heap_buf: When @flags & %EFX_TX_BUF_HEAP, the associated heap buffer to be
* freed when descriptor completes.
* @dma_addr: DMA address of the fragment.
* @flags: Flags for allocation and DMA mapping type
* @len: Length of this fragment.
@@ -104,7 +105,7 @@ struct efx_special_buffer {
struct efx_tx_buffer {
union {
const struct sk_buff *skb;
struct efx_tso_header *tsoh;
void *heap_buf;
};
dma_addr_t dma_addr;
unsigned short flags;
@@ -113,7 +114,7 @@ struct efx_tx_buffer {
};
#define EFX_TX_BUF_CONT 1 /* not last descriptor of packet */
#define EFX_TX_BUF_SKB 2 /* buffer is last part of skb */
#define EFX_TX_BUF_TSOH 4 /* buffer is TSO header */
#define EFX_TX_BUF_HEAP 4 /* buffer was allocated with kmalloc() */
#define EFX_TX_BUF_MAP_SINGLE 8 /* buffer was mapped with dma_map_single() */
/**
@@ -134,6 +135,7 @@ struct efx_tx_buffer {
* @channel: The associated channel
* @core_txq: The networking core TX queue structure
* @buffer: The software buffer ring
* @tsoh_page: Array of pages of TSO header buffers
* @txd: The hardware descriptor ring
* @ptr_mask: The size of the ring minus 1.
* @initialised: Has hardware queue been initialised?
@@ -157,9 +159,6 @@ struct efx_tx_buffer {
* variable indicates that the queue is full. This is to
* avoid cache-line ping-pong between the xmit path and the
* completion path.
* @tso_headers_free: A list of TSO headers allocated for this TX queue
* that are not in use, and so available for new TSO sends. The list
* is protected by the TX queue lock.
* @tso_bursts: Number of times TSO xmit invoked by kernel
* @tso_long_headers: Number of packets with headers too long for standard
* blocks
@@ -176,6 +175,7 @@ struct efx_tx_queue {
struct efx_channel *channel;
struct netdev_queue *core_txq;
struct efx_tx_buffer *buffer;
struct efx_buffer *tsoh_page;
struct efx_special_buffer txd;
unsigned int ptr_mask;
bool initialised;
@@ -188,7 +188,6 @@ struct efx_tx_queue {
unsigned int insert_count ____cacheline_aligned_in_smp;
unsigned int write_count;
unsigned int old_read_count;
struct efx_tso_header *tso_headers_free;
unsigned int tso_bursts;
unsigned int tso_long_headers;
unsigned int tso_packets;