On Wed, Jul 24, 2024 at 10:35 AM Praveen Kaligineedi
<pkaligineedi@xxxxxxxxxx> wrote:
>
> From: Bailey Forrest <bcf@xxxxxxxxxx>
>
> The NIC requires each TSO segment to not span more than 10
> descriptors. NIC further requires each descriptor to not exceed
> 16KB - 1 (GVE_TX_MAX_BUF_SIZE_DQO).
>
> The descriptors for an skb are generated by
> gve_tx_add_skb_no_copy_dqo() for DQO RDA queue format.
> gve_tx_add_skb_no_copy_dqo() loops through each skb frag and
> generates a descriptor for the entire frag if the frag size is
> not greater than GVE_TX_MAX_BUF_SIZE_DQO. If the frag size is
> greater than GVE_TX_MAX_BUF_SIZE_DQO, it is split into descriptor(s)
> of size GVE_TX_MAX_BUF_SIZE_DQO and a descriptor is generated for
> the remainder (frag size % GVE_TX_MAX_BUF_SIZE_DQO).
>
> gve_can_send_tso() checks if the descriptors thus generated for an
> skb would meet the requirement that each TSO-segment not span more
> than 10 descriptors. However, the current code misses an edge case
> when a TSO segment spans multiple descriptors within a large frag.
> This change fixes the edge case.
>
> gve_can_send_tso() relies on the assumption that max gso size (9728)
> is less than GVE_TX_MAX_BUF_SIZE_DQO and therefore within an skb
> fragment a TSO segment can never span more than 2 descriptors.
>
> Fixes: a57e5de476be ("gve: DQO: Add TX path")
> Signed-off-by: Praveen Kaligineedi <pkaligineedi@xxxxxxxxxx>
> Signed-off-by: Bailey Forrest <bcf@xxxxxxxxxx>
> Reviewed-by: Jeroen de Borst <jeroendb@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Thanks for the extra description. The way gve_tx_add_skb_no_copy_dqo
lays out descriptors, and the descriptor and segment max lengths are key.
Now I follow the calculation.
