On Thu, Feb 06, 2025 at 02:04:07PM +0800, Song Yoong Siang wrote:
> Refactor the code for inserting an empty frame into a new function
> igc_insert_empty_frame(). This change extracts the logic for inserting
> an empty packet from igc_xmit_frame_ring() into a separate function,
> allowing it to be reused in future implementations, such as the XDP
> zero copy transmit function.
>
> Remove the igc_desc_unused() checking in igc_init_tx_empty_descriptor()
> because the number of descriptors needed is guaranteed.
>
> Ensure that skb allocation and DMA mapping work for the empty frame,
> before proceeding to fill in igc_tx_buffer info, context descriptor,
> and data descriptor.
>
> Rate limit the error messages for skb allocation and DMA mapping failures.
>
> Update the comment to indicate that the 2 descriptors needed by the empty
> frame are already taken into consideration in igc_xmit_frame_ring().
>
> Handle the case where the insertion of an empty frame fails and explain
> the reason behind this handling.
>
> Signed-off-by: Song Yoong Siang <yoong.siang.song@xxxxxxxxx>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx>
with one nit below.
> ---
> drivers/net/ethernet/intel/igc/igc_main.c | 84 ++++++++++++++---------
> 1 file changed, 52 insertions(+), 32 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
> index 84307bb7313e..3df608601a4b 100644
> --- a/drivers/net/ethernet/intel/igc/igc_main.c
> +++ b/drivers/net/ethernet/intel/igc/igc_main.c
> @@ -1092,7 +1092,9 @@ static int igc_init_empty_frame(struct igc_ring *ring,
>
> dma = dma_map_single(ring->dev, skb->data, size, DMA_TO_DEVICE);
> if (dma_mapping_error(ring->dev, dma)) {
> - netdev_err_once(ring->netdev, "Failed to map DMA for TX\n");
> + if (net_ratelimit())
> + netdev_err(ring->netdev,
> + "DMA mapping error for empty frame\n");
This is open-coded net_err_ratelimited(), no?
> return -ENOMEM;
> }
>
> @@ -1108,20 +1110,12 @@ static int igc_init_empty_frame(struct igc_ring *ring,
> return 0;
> }
>
> -static int igc_init_tx_empty_descriptor(struct igc_ring *ring,
> - struct sk_buff *skb,
> - struct igc_tx_buffer *first)
> +static void igc_init_tx_empty_descriptor(struct igc_ring *ring,
> + struct sk_buff *skb,
> + struct igc_tx_buffer *first)
> {
> union igc_adv_tx_desc *desc;
> u32 cmd_type, olinfo_status;
> - int err;
> -
> - if (!igc_desc_unused(ring))
> - return -EBUSY;
> -
> - err = igc_init_empty_frame(ring, first, skb);
> - if (err)
> - return err;
>
> cmd_type = IGC_ADVTXD_DTYP_DATA | IGC_ADVTXD_DCMD_DEXT |
> IGC_ADVTXD_DCMD_IFCS | IGC_TXD_DCMD |
> @@ -1140,8 +1134,6 @@ static int igc_init_tx_empty_descriptor(struct igc_ring *ring,
> ring->next_to_use++;
> if (ring->next_to_use == ring->count)
> ring->next_to_use = 0;
> -
> - return 0;
> }
>
> #define IGC_EMPTY_FRAME_SIZE 60
> @@ -1567,6 +1559,41 @@ static bool igc_request_tx_tstamp(struct igc_adapter *adapter, struct sk_buff *s
> return false;
> }
>
> +static int igc_insert_empty_frame(struct igc_ring *tx_ring)
> +{
> + struct igc_tx_buffer *empty_info;
> + struct sk_buff *empty_skb;
> + void *data;
> + int ret;
> +
> + empty_info = &tx_ring->tx_buffer_info[tx_ring->next_to_use];
> + empty_skb = alloc_skb(IGC_EMPTY_FRAME_SIZE, GFP_ATOMIC);
> + if (unlikely(!empty_skb)) {
> + if (net_ratelimit())
> + netdev_err(tx_ring->netdev,
> + "skb alloc error for empty frame\n");
ditto
> + return -ENOMEM;
> + }
> +
> + data = skb_put(empty_skb, IGC_EMPTY_FRAME_SIZE);
> + memset(data, 0, IGC_EMPTY_FRAME_SIZE);
> +
> + /* Prepare DMA mapping and Tx buffer information */
> + ret = igc_init_empty_frame(tx_ring, empty_info, empty_skb);
> + if (unlikely(ret)) {
> + dev_kfree_skb_any(empty_skb);
> + return ret;
> + }
> +
> + /* Prepare advanced context descriptor for empty packet */
> + igc_tx_ctxtdesc(tx_ring, 0, false, 0, 0, 0);
> +
> + /* Prepare advanced data descriptor for empty packet */
> + igc_init_tx_empty_descriptor(tx_ring, empty_skb, empty_info);
> +
> + return 0;
> +}
> +
> static netdev_tx_t igc_xmit_frame_ring(struct sk_buff *skb,
> struct igc_ring *tx_ring)
> {
> @@ -1586,6 +1613,7 @@ static netdev_tx_t igc_xmit_frame_ring(struct sk_buff *skb,
> * + 1 desc for skb_headlen/IGC_MAX_DATA_PER_TXD,
> * + 2 desc gap to keep tail from touching head,
> * + 1 desc for context descriptor,
> + * + 2 desc for inserting an empty packet for launch time,
> * otherwise try next time
> */
> for (f = 0; f < skb_shinfo(skb)->nr_frags; f++)
> @@ -1605,24 +1633,16 @@ static netdev_tx_t igc_xmit_frame_ring(struct sk_buff *skb,
> launch_time = igc_tx_launchtime(tx_ring, txtime, &first_flag, &insert_empty);
>
> if (insert_empty) {
> - struct igc_tx_buffer *empty_info;
> - struct sk_buff *empty;
> - void *data;
> -
> - empty_info = &tx_ring->tx_buffer_info[tx_ring->next_to_use];
> - empty = alloc_skb(IGC_EMPTY_FRAME_SIZE, GFP_ATOMIC);
> - if (!empty)
> - goto done;
> -
> - data = skb_put(empty, IGC_EMPTY_FRAME_SIZE);
> - memset(data, 0, IGC_EMPTY_FRAME_SIZE);
> -
> - igc_tx_ctxtdesc(tx_ring, 0, false, 0, 0, 0);
> -
> - if (igc_init_tx_empty_descriptor(tx_ring,
> - empty,
> - empty_info) < 0)
> - dev_kfree_skb_any(empty);
> + /* Reset the launch time if the required empty frame fails to
> + * be inserted. However, this packet is not dropped, so it
> + * "dirties" the current Qbv cycle. This ensures that the
> + * upcoming packet, which is scheduled in the next Qbv cycle,
> + * does not require an empty frame. This way, the launch time
> + * continues to function correctly despite the current failure
> + * to insert the empty frame.
> + */
> + if (igc_insert_empty_frame(tx_ring))
> + launch_time = 0;
> }
>
> done:
> --
> 2.34.1
>
