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

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Message-ID: <CAL+tcoBQvDJO8n7npQjzKBd6HEZ8KhE08g4hRhqokU-bpTe6tw@mail.gmail.com>
Date: Wed, 25 Jun 2025 08:19:01 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
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 Wed, Jun 25, 2025 at 7:31 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> 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

Ah, my fault. Thanks for reminding me. I missed the 'refilling budget'
process...
For the record:
xsk_tx_peek_desc()
    -> xs->tx_budget_spent = 0;

> again.
>
> For the ZC case the true budget is set by the driver's NAPI loop.

True.

I will remove this one.

Thanks,
Jason

> --
> pw-bot: cr