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

[Björn Töpel]

On Thu, 18 Feb 2021 at 15:15, Jason A. Donenfeld <Jason at zx2c4.com> wrote:
>

[...]

> >
> > > +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!
>
> The downside is that on armv7, this becomes a dmb(ish) instead of a
> dmb(ishst). But I was unable to measure any actual difference anyway,
> and the atomic bounded increment is already more expensive, so I think
> it's okay.
>

Who cares about armv7!? The world is moving to Armv8/LSE, where we'll
end up with one fine "swpl" in this case, w/o any explicit (well...)
fence. ;-P

On a more serious note, it does make sense to base the decision on
benchmarks. OTOH I'd guess that the systems that mostly benefit from
this memory saving patch are x86_64, where the
smp_wmb()/xchg_relaxed() and xchg_release() are identical.


Björn