netdev - Re: [PATCH net-next 1/2] xsk: avoid using heavy lock when the pool is not shared

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Message-ID: <CAL+tcoDJ00BzKAta6=M0K9JkoT80DVkSDvevGug28b7RrTf6hQ@mail.gmail.com>
Date: Wed, 29 Oct 2025 09:36:47 +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, 
	horms@...nel.org, andrew+netdev@...n.ch, bpf@...r.kernel.org, 
	netdev@...r.kernel.org, Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next 1/2] xsk: avoid using heavy lock when the pool is
 not shared

On Wed, Oct 29, 2025 at 8:29 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Sat, 25 Oct 2025 14:53:09 +0800 Jason Xing wrote:
> >  static int xsk_cq_reserve_locked(struct xsk_buff_pool *pool)
> >  {
> > +     bool lock = !list_is_singular(&pool->xsk_tx_list);
> >       unsigned long flags;
> >       int ret;
> >
> > -     spin_lock_irqsave(&pool->cq_lock, flags);
> > +     if (lock)
> > +             spin_lock_irqsave(&pool->cq_lock, flags);
> >       ret = xskq_prod_reserve(pool->cq);
> > -     spin_unlock_irqrestore(&pool->cq_lock, flags);
> > +     if (lock)
> > +             spin_unlock_irqrestore(&pool->cq_lock, flags);
>
> Please explain in the commit message what guarantees that the list will
> remain singular until the function exits.

Thanks for bringing up a good point that I missed before. I think I
might acquire xsk_tx_list_lock first to make sure xp_add_xsk() will
not interfere with this process. I will figure it out soon.

Thanks,
Jason

> --
> pw-bot: cr