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SubjectRe: [PATCH net-next v2 02/12] net: stmmac: Prepare to add Split Header support
On Mon, 12 Aug 2019 11:44:01 +0200, Jose Abreu wrote:
> In order to add Split Header support, stmmac_rx() needs to take into
> account that packet may be split accross multiple descriptors.
>
> Refactor the logic of this function in order to support this scenario.
>
> Signed-off-by: Jose Abreu <joabreu@synopsys.com>
>
> ---
> Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
> Cc: Alexandre Torgue <alexandre.torgue@st.com>
> Cc: Jose Abreu <joabreu@synopsys.com>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
> Cc: netdev@vger.kernel.org
> Cc: linux-stm32@st-md-mailman.stormreply.com
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> ---
> drivers/net/ethernet/stmicro/stmmac/stmmac.h | 6 +
> drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 149 +++++++++++++---------
> 2 files changed, 95 insertions(+), 60 deletions(-)
>
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
> index 80276587048a..56158e1448ac 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
> @@ -74,6 +74,12 @@ struct stmmac_rx_queue {
> u32 rx_zeroc_thresh;
> dma_addr_t dma_rx_phy;
> u32 rx_tail_addr;
> + unsigned int state_saved;
> + struct {
> + struct sk_buff *skb;
> + unsigned int len;
> + unsigned int error;
> + } state;
> };
>
> struct stmmac_channel {
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index b2e5f4ecd551..a093eb4ec275 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -3353,9 +3353,10 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
> {
> struct stmmac_rx_queue *rx_q = &priv->rx_queue[queue];
> struct stmmac_channel *ch = &priv->channel[queue];
> + unsigned int count = 0, error = 0, len = 0;
> + int status = 0, coe = priv->hw->rx_csum;
> unsigned int next_entry = rx_q->cur_rx;
> - int coe = priv->hw->rx_csum;
> - unsigned int count = 0;
> + struct sk_buff *skb = NULL;
>
> if (netif_msg_rx_status(priv)) {
> void *rx_head;
> @@ -3369,9 +3370,27 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
> stmmac_display_ring(priv, rx_head, DMA_RX_SIZE, true);
> }
> while (count < limit) {
> + enum pkt_hash_types hash_type;
> struct stmmac_rx_buffer *buf;
> + unsigned int prev_len = 0;
> struct dma_desc *np, *p;
> - int entry, status;
> + int entry;
> + u32 hash;
> +
> + if (!count && rx_q->state_saved) {
> + skb = rx_q->state.skb;
> + error = rx_q->state.error;
> + len = rx_q->state.len;
> + } else {
> + rx_q->state_saved = false;
> + skb = NULL;
> + error = 0;
> + len = 0;
> + }
> +
> +read_again:
> + if (count >= limit)
> + break;

Is this stopping the NAPI poll once @limit descriptors were seen?
It should probably be okay to ignore the limit until you get a full
frame? I'd think it'd be best to finish up the frame while the state
is hot in the CPU cache.. WDYT?

> entry = next_entry;
> buf = &rx_q->buf_pool[entry];
> @@ -3407,28 +3426,24 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
> page_pool_recycle_direct(rx_q->page_pool, buf->page);
> priv->dev->stats.rx_errors++;
> buf->page = NULL;
> + error = 1;
> + }
> +
> + if (unlikely(error & (status & rx_not_ls)))

Looks suspicious - sure this is supposed to be error & (status & bla)
and not error && ... ?

> + goto read_again;
> + if (unlikely(error)) {
> + if (skb)
> + dev_kfree_skb(skb);
> + continue;
> + }
> +
> + /* Buffer is good. Go on. */
> +
> + if (likely(status & rx_not_ls)) {
> + len += priv->dma_buf_sz;
> } else {
> - enum pkt_hash_types hash_type;
> - struct sk_buff *skb;
> - unsigned int des;
> - int frame_len;
> - u32 hash;
> -
> - stmmac_get_desc_addr(priv, p, &des);
> - frame_len = stmmac_get_rx_frame_len(priv, p, coe);
> -
> - /* If frame length is greater than skb buffer size
> - * (preallocated during init) then the packet is
> - * ignored
> - */
> - if (frame_len > priv->dma_buf_sz) {
> - if (net_ratelimit())
> - netdev_err(priv->dev,
> - "len %d larger than size (%d)\n",
> - frame_len, priv->dma_buf_sz);
> - priv->dev->stats.rx_length_errors++;
> - continue;
> - }
> + prev_len = len;
> + len = stmmac_get_rx_frame_len(priv, p, coe);
>
> /* ACS is set; GMAC core strips PAD/FCS for IEEE 802.3
> * Type frames (LLC/LLC-SNAP)
> @@ -3439,57 +3454,71 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
> */
> if (unlikely(priv->synopsys_id >= DWMAC_CORE_4_00) ||
> unlikely(status != llc_snap))
> - frame_len -= ETH_FCS_LEN;
> -
> - if (netif_msg_rx_status(priv)) {
> - netdev_dbg(priv->dev, "\tdesc: %p [entry %d] buff=0x%x\n",
> - p, entry, des);
> - netdev_dbg(priv->dev, "frame size %d, COE: %d\n",
> - frame_len, status);
> - }
> + len -= ETH_FCS_LEN;
> + }
>
> - skb = netdev_alloc_skb_ip_align(priv->dev, frame_len);
> - if (unlikely(!skb)) {
> + if (!skb) {
> + skb = netdev_alloc_skb_ip_align(priv->dev, len);

Since you're in NAPI call perhaps something like napi_alloc_skb() could
speed things up a little? But please also see below..

> + if (!skb) {
> priv->dev->stats.rx_dropped++;
> continue;
> }
>
> - dma_sync_single_for_cpu(priv->device, buf->addr,
> - frame_len, DMA_FROM_DEVICE);
> + dma_sync_single_for_cpu(priv->device, buf->addr, len,
> + DMA_FROM_DEVICE);
> skb_copy_to_linear_data(skb, page_address(buf->page),
> - frame_len);
> - skb_put(skb, frame_len);
> + len);
> + skb_put(skb, len);
>
> - if (netif_msg_pktdata(priv)) {
> - netdev_dbg(priv->dev, "frame received (%dbytes)",
> - frame_len);
> - print_pkt(skb->data, frame_len);
> - }
> + /* Data payload copied into SKB, page ready for recycle */
> + page_pool_recycle_direct(rx_q->page_pool, buf->page);
> + buf->page = NULL;
> + } else {
> + unsigned int buf_len = len - prev_len;
>
> - stmmac_get_rx_hwtstamp(priv, p, np, skb);
> + if (likely(status & rx_not_ls))
> + buf_len = priv->dma_buf_sz;
>
> - stmmac_rx_vlan(priv->dev, skb);
> + dma_sync_single_for_cpu(priv->device, buf->addr,
> + buf_len, DMA_FROM_DEVICE);
> + skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
> + buf->page, 0, buf_len,
> + priv->dma_buf_sz);
>
> - skb->protocol = eth_type_trans(skb, priv->dev);
> + /* Data payload appended into SKB */
> + page_pool_release_page(rx_q->page_pool, buf->page);
> + buf->page = NULL;
> + }
>
> - if (unlikely(!coe))
> - skb_checksum_none_assert(skb);
> - else
> - skb->ip_summed = CHECKSUM_UNNECESSARY;
> + if (likely(status & rx_not_ls))
> + goto read_again;
>
> - if (!stmmac_get_rx_hash(priv, p, &hash, &hash_type))
> - skb_set_hash(skb, hash, hash_type);
> + /* Got entire packet into SKB. Finish it. */
>
> - skb_record_rx_queue(skb, queue);
> - napi_gro_receive(&ch->rx_napi, skb);
> + stmmac_get_rx_hwtstamp(priv, p, np, skb);
> + stmmac_rx_vlan(priv->dev, skb);
> + skb->protocol = eth_type_trans(skb, priv->dev);
>
> - /* Data payload copied into SKB, page ready for recycle */
> - page_pool_recycle_direct(rx_q->page_pool, buf->page);
> - buf->page = NULL;
> + if (unlikely(!coe))
> + skb_checksum_none_assert(skb);
> + else
> + skb->ip_summed = CHECKSUM_UNNECESSARY;
>
> - priv->dev->stats.rx_packets++;
> - priv->dev->stats.rx_bytes += frame_len;
> - }
> + if (!stmmac_get_rx_hash(priv, p, &hash, &hash_type))
> + skb_set_hash(skb, hash, hash_type);
> +
> + skb_record_rx_queue(skb, queue);
> + napi_gro_receive(&ch->rx_napi, skb);

Did you look into using napi_gro_frags() family of APIs?
I think Eric said those are more efficient from GRO perspective..

> + priv->dev->stats.rx_packets++;
> + priv->dev->stats.rx_bytes += len;
> + }
> +
> + if (status & rx_not_ls) {
> + rx_q->state_saved = true;
> + rx_q->state.skb = skb;
> + rx_q->state.error = error;
> + rx_q->state.len = len;
> }
>
> stmmac_rx_refill(priv, queue);

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