[email protected] wrote:
> From: Steve Chen <[[email protected]]>
>
> The skb data allocated for packet data received is 4 byte aligned.
>
> Unfortunately, this causes non-32bit aligned accesses in IP stack because
> the MAC header is non-word aligned (14 bytes).
>
> The result can be observed by looking at /proc/cpu/alignment while the
> device is over network.
>
> This issue is resolved by using a 2-byte extra offset in the packet buffer.
>
> A quick performance test over lab network using iperf on DM6446 EVM showed
> an increase in bandwidth from 60Mbits/s to 70Mbits/s.
>
> Signed-off-by: Steve Chen <[email protected]>
> Acked-by: Sekhar Nori <[email protected]>
> Signed-off-by: Sekhar Nori <[email protected]>
> ---
> drivers/net/davinci_emac.c | 23 +++++++++++++++++++----
> 1 files changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/davinci_emac.c b/drivers/net/davinci_emac.c
> index 635e31f..eecd983 100644
> --- a/drivers/net/davinci_emac.c
> +++ b/drivers/net/davinci_emac.c
> @@ -349,6 +349,17 @@ static const char emac_version_string[] = "TI DaVinci
> EMAC Linux v6.0";
> #define EMAC_DM646X_MAC_EOI_C0_RXEN (0x01)
> #define EMAC_DM646X_MAC_EOI_C0_TXEN (0x02)
>
> +/*
> + * L3 Alignment mechanism: The below given macro returns the number of
> + * bytes required to align the given size to a L3 frame 4 byte
> + * boundry. This is typically required to add 2 bytes to the ethernet
> + * frame start to make sure the IP header (L3) is aligned on a 4 byte
> + * boundry
> + */
> +static char emac_L3_align[] = { 0x02, 0x01, 0x00, 0x03 };
> +
> +#define EMAC_L3_ALIGN(size) emac_L3_align[(size) & 0x3]
How about
#define EMAC_L3_ALIGN(size) (((2-(size)) & 0x3)
> +
> /** net_buf_obj: EMAC network bufferdata structure
> *
> * EMAC network buffer data structure
> @@ -1560,7 +1571,8 @@ static void *emac_net_alloc_rx_buf(struct emac_priv
> *priv, int buf_size,
>
> /* set device pointer in skb and reserve space for extra bytes */
> p_skb->dev = ndev;
> - skb_reserve(p_skb, EMAC_DEF_EXTRA_RXBUF_SIZE);
> + skb_reserve(p_skb, EMAC_DEF_EXTRA_RXBUF_SIZE +
> + EMAC_L3_ALIGN(EMAC_DEF_EXTRA_RXBUF_SIZE));
> *data_token = (void *) p_skb;
> EMAC_CACHE_WRITEBACK_INVALIDATE((unsigned long)p_skb->data, buf_size);
> return p_skb->data;
> @@ -1990,8 +2002,9 @@ static int emac_rx_bdproc(struct emac_priv *priv, u32
> ch, u32 budget,
> (pkts_processed < budget)) {
>
> new_buffer = emac_net_alloc_rx_buf(priv,
> - EMAC_DEF_MAX_FRAME_SIZE,
> - &new_buf_token, EMAC_DEF_RX_CH);
> + EMAC_DEF_MAX_FRAME_SIZE +
> + EMAC_L3_ALIGN(EMAC_DEF_EXTRA_RXBUF_SIZE),
> + &new_buf_token, EMAC_DEF_RX_CH);
> if (unlikely(NULL == new_buffer)) {
> ++rxch->out_of_rx_buffers;
> goto end_emac_rx_bdproc;
> @@ -2411,7 +2424,9 @@ static int emac_dev_open(struct net_device *ndev)
> ndev->dev_addr[cnt] = priv->mac_addr[cnt];
>
> /* Configuration items */
> - priv->rx_buf_size = EMAC_DEF_MAX_FRAME_SIZE + EMAC_DEF_EXTRA_RXBUF_SIZE;
> + priv->rx_buf_size = EMAC_DEF_MAX_FRAME_SIZE +
> + EMAC_DEF_EXTRA_RXBUF_SIZE +
> + EMAC_L3_ALIGN(EMAC_DEF_EXTRA_RXBUF_SIZE);
>
> /* Clear basic hardware */
> for (ch = 0; ch < EMAC_MAX_TXRX_CHANNELS; ch++) {
Thanks for the improvement!
Troy
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