From: "Björn Töpel" <bjorn@kernel.org>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: WireGuard mailing list <wireguard@lists.zx2c4.com>,
Dmitry Vyukov <dvyukov@google.com>
Subject: Re: [PATCH RFC v1] wireguard: queueing: get rid of per-peer ring buffers
Date: Thu, 18 Feb 2021 16:12:49 +0100 [thread overview]
Message-ID: <CAJ+HfNi2Bdi-xa+rsgxWkxFdykM1CKznGMdj=FoazEbNh1m4Dw@mail.gmail.com> (raw)
In-Reply-To: <CAHmME9qf_EY8xTi81VPr9O9_95HpdjxobLtd1=C7fK2kRUxWiw@mail.gmail.com>
On Thu, 18 Feb 2021 at 15:15, Jason A. Donenfeld <Jason@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
prev parent reply other threads:[~2021-02-18 15:13 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-08 13:38 [PATCH RFC v1] wireguard: queueing: get rid of per-peer ring buffers Jason A. Donenfeld
2021-02-09 8:24 ` Dmitry Vyukov
2021-02-09 15:44 ` Jason A. Donenfeld
2021-02-09 16:20 ` Dmitry Vyukov
2021-02-17 18:36 ` Toke Høiland-Jørgensen
2021-02-17 22:28 ` Jason A. Donenfeld
2021-02-17 23:41 ` Toke Høiland-Jørgensen
2021-02-18 13:49 ` Björn Töpel
2021-02-18 13:53 ` Jason A. Donenfeld
2021-02-18 14:04 ` Björn Töpel
2021-02-18 14:15 ` Jason A. Donenfeld
2021-02-18 15:12 ` Björn Töpel [this message]
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