On Mon, 23 Oct 2023 at 14:57, Albert Huang
<huangjie.albert@xxxxxxxxxxxxx> wrote:
>
> In the previous implementation, when multiple xsk sockets were
> associated with a single xsk_buff_pool, a situation could arise
> where the xsk_tx_list maintained data at the front for one xsk
> socket while starving the xsk sockets at the back of the list.
> This could result in issues such as the inability to transmit packets,
> increased latency, and jitter. To address this problem, we introduce
> a new variable called tx_budget_spent, which limits each xsk to transmit
> a maximum of MAX_PER_SOCKET_BUDGET tx descriptors. This allocation ensures
> equitable opportunities for subsequent xsk sockets to send tx descriptors.
> The value of MAX_PER_SOCKET_BUDGET is set to 32.
Thank you Albert for implementing this feature!
Acked-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
> Signed-off-by: Albert Huang <huangjie.albert@xxxxxxxxxxxxx>
> ---
> include/net/xdp_sock.h | 7 +++++++
> net/xdp/xsk.c | 18 ++++++++++++++++++
> 2 files changed, 25 insertions(+)
>
> diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
> index 69b472604b86..de6819e50d54 100644
> --- a/include/net/xdp_sock.h
> +++ b/include/net/xdp_sock.h
> @@ -63,6 +63,13 @@ struct xdp_sock {
>
> struct xsk_queue *tx ____cacheline_aligned_in_smp;
> struct list_head tx_list;
> + /* record the number of tx descriptors sent by this xsk and
> + * when it exceeds MAX_PER_SOCKET_BUDGET, an opportunity needs
> + * to be given to other xsks for sending tx descriptors, thereby
> + * preventing other XSKs from being starved.
> + */
> + u32 tx_budget_spent;
> +
> /* Protects generic receive. */
> spinlock_t rx_lock;
>
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index f5e96e0d6e01..65c32b85c326 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -33,6 +33,7 @@
> #include "xsk.h"
>
> #define TX_BATCH_SIZE 32
> +#define MAX_PER_SOCKET_BUDGET (TX_BATCH_SIZE)
>
> static DEFINE_PER_CPU(struct list_head, xskmap_flush_list);
>
> @@ -413,16 +414,25 @@ EXPORT_SYMBOL(xsk_tx_release);
>
> bool xsk_tx_peek_desc(struct xsk_buff_pool *pool, struct xdp_desc *desc)
> {
> + bool budget_exhausted = false;
> struct xdp_sock *xs;
>
> rcu_read_lock();
> +again:
> list_for_each_entry_rcu(xs, &pool->xsk_tx_list, tx_list) {
> + if (xs->tx_budget_spent >= MAX_PER_SOCKET_BUDGET) {
> + budget_exhausted = true;
> + continue;
> + }
> +
> if (!xskq_cons_peek_desc(xs->tx, desc, pool)) {
> if (xskq_has_descs(xs->tx))
> xskq_cons_release(xs->tx);
> continue;
> }
>
> + xs->tx_budget_spent++;
> +
> /* This is the backpressure mechanism for the Tx path.
> * Reserve space in the completion queue and only proceed
> * if there is space in it. This avoids having to implement
> @@ -436,6 +446,14 @@ bool xsk_tx_peek_desc(struct xsk_buff_pool *pool, struct xdp_desc *desc)
> return true;
> }
>
> + if (budget_exhausted) {
> + list_for_each_entry_rcu(xs, &pool->xsk_tx_list, tx_list)
> + xs->tx_budget_spent = 0;
> +
> + budget_exhausted = false;
> + goto again;
> + }
> +
> out:
> rcu_read_unlock();
> return false;
> --
> 2.20.1
>
>
