netdev - Re: [PATCH net-next v4] net: xsk: introduce XDP_MAX_TX

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Message-ID: <20250624163114.712a9c43@kernel.org>
Date: Tue, 24 Jun 2025 16:31:14 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
 bjorn@...nel.org, magnus.karlsson@...el.com, maciej.fijalkowski@...el.com,
 jonathan.lemon@...il.com, sdf@...ichev.me, ast@...nel.org,
 daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
 joe@...a.to, willemdebruijn.kernel@...il.com, bpf@...r.kernel.org,
 netdev@...r.kernel.org, Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v4] net: xsk: introduce XDP_MAX_TX_BUDGET
 setsockopt

On Mon, 23 Jun 2025 10:13:45 +0800 Jason Xing wrote:
> @@ -424,7 +421,9 @@ bool xsk_tx_peek_desc(struct xsk_buff_pool *pool, struct xdp_desc *desc)
>  	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) {
> +		int max_budget = READ_ONCE(xs->max_tx_budget);
> +
> +		if (xs->tx_budget_spent >= max_budget) {
>  			budget_exhausted = true;
>  			continue;
>  		}

I still think you're mixing two very different things. In the generic
xmit path the value you're changing is a budget. But xsk_tx_peek_desc()
*does not* exit after the "per socket budget" gets spent. The per
socket budget only controls how many frames we pick from a single sock
before we move to the next. But if we run out of budget on all sockets
we give every socket a full budget again and start from the first one
again.

For the ZC case the true budget is set by the driver's NAPI loop.
-- 
pw-bot: cr