[PATCH RFC v1] wireguard: queueing: get rid of per-peer ring buffers

[Björn Töpel]

On Thu, 18 Feb 2021 at 14:53, Jason A. Donenfeld <Jason at zx2c4.com> wrote:
>
> Hey Bjorn,
>
> On Thu, Feb 18, 2021 at 2:50 PM Björn Töpel <bjorn at kernel.org> wrote:
> > > +
> > > +static void __wg_prev_queue_enqueue(struct prev_queue *queue, struct sk_buff *skb)
> > > +{
> > > +       WRITE_ONCE(NEXT(skb), NULL);
> > > +       smp_wmb();
> > > +       WRITE_ONCE(NEXT(xchg_relaxed(&queue->head, skb)), skb);
> > > +}
> > > +
> >
> > I'll chime in with Toke; This MPSC and Dmitry's links really took me
> > to the "verify with pen/paper"-level! Thanks!
> >
> > I'd replace the smp_wmb()/_relaxed above with a xchg_release(), which
> > might perform better on some platforms. Also, it'll be a nicer pair
> > with the ldacq below. :-P In general, it would be nice with some
> > wording how the fences pair. It would help the readers (like me!) a
> > lot.
>
> Exactly. This is what's been in my dev tree for the last week or so:
>

Ah, nice!

> +static void __wg_prev_queue_enqueue(struct prev_queue *queue, struct
> sk_buff *skb)
> +{
> +       WRITE_ONCE(NEXT(skb), NULL);
> +       WRITE_ONCE(NEXT(xchg_release(&queue->head, skb)), skb);
> +}
>
> Look good?
>

Yes, exactly like that!


Cheers,
Björn