xsk: Avoid starving the xsk further down the list

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.

Signed-off-by: Albert Huang <huangjie.albert@bytedance.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/bpf/20231023125732.82261-1-huangjie.albert@bytedance.com

1 files changed, 7 insertions, 0 deletions

diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
index 7dd0df2f6f8e..f83128007fb0 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;