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Message-ID: <1482165628.1521.9.camel@edumazet-glaptop3.roam.corp.google.com> Date: Mon, 19 Dec 2016 08:40:28 -0800 From: Eric Dumazet <eric.dumazet@...il.com> To: Hannes Frederic Sowa <hannes@...essinduktion.org> Cc: Julian Anastasov <ja@....bg>, netdev@...r.kernel.org, linux-sctp@...r.kernel.org, YueHaibing <yuehaibing@...wei.com> Subject: Re: [PATCH RFC net-next 2/7] net: add dst_pending_confirm flag to skbuff On Mon, 2016-12-19 at 17:36 +0100, Hannes Frederic Sowa wrote: > On 19.12.2016 17:17, Eric Dumazet wrote: > > On Sun, 2016-12-18 at 22:56 +0200, Julian Anastasov wrote: > > > >> > >> +static inline void sock_confirm_neigh(struct sk_buff *skb, struct neighbour *n) > >> +{ > >> + if (unlikely(skb->dst_pending_confirm)) { > >> + struct sock *sk = skb->sk; > >> + unsigned long now = jiffies; > >> + > >> + /* avoid dirtying neighbour */ > >> + if (n->confirmed != now) > >> + n->confirmed = now; > >> + if (sk && sk->sk_dst_pending_confirm) > >> + sk->sk_dst_pending_confirm = 0; > >> + } > >> +} > >> + > > > > I am still digesting this awesome patch series ;) > > > > Not sure why you used an unlikely() here. TCP for example would hit this > > path quite often. > > > > So considering sk_dst_pending_confirm might be dirtied quite often, > > > > I am not sure why you placed it in the cache line that contains > > sk_rx_dst (in 1st patch) > > Because they have to stay synchronized? > > If we modify sk_rx_dst, we automatically also must clear > pending_confirm, otherwise we might end up confirming a wrong neighbor. Your answer makes little sense really... For most TCP flows, we set sk_rx_dst exactly once. Hardly a good reason to have these in the same cache line.
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