From 99b29a499b5fdfb7ab274835b8e4d4c11df2f6d7 Mon Sep 17 00:00:00 2001 From: Albert Huang Date: Mon, 23 Oct 2023 20:57:31 +0800 Subject: 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 Signed-off-by: Daniel Borkmann Acked-by: Magnus Karlsson Link: https://lore.kernel.org/bpf/20231023125732.82261-1-huangjie.albert@bytedance.com --- net/xdp/xsk.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'net/xdp') diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index ba070fd37d24..ae9f8cb611f6 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); @@ -423,16 +424,25 @@ 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 @@ -446,6 +456,14 @@ 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; -- cgit v1.2.3-70-g09d2