Re: [PATCH v3 net-next] net-core: add rx_otherhost_dropped counter

[Eric Dumazet]

On Tue, Mar 8, 2022 at 2:51 PM David Ahern <dsahern@xxxxxxxxxx> wrote:
>
> On 3/8/22 2:25 PM, Jeffrey Ji wrote:
> > diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
> > index 95f7bb052784..8b87ea99904b 100644
> > --- a/net/ipv4/ip_input.c
> > +++ b/net/ipv4/ip_input.c
> > @@ -451,6 +451,7 @@ static struct sk_buff *ip_rcv_core(struct sk_buff *skb, struct net *net)
> >        * that it receives, do not try to analyse it.
> >        */
> >       if (skb->pkt_type == PACKET_OTHERHOST) {
> > +             atomic_long_inc(&skb->dev->rx_otherhost_dropped);
> >               drop_reason = SKB_DROP_REASON_OTHERHOST;
> >               goto drop;
> >       }
> > diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c
> > index 5b5ea35635f9..5624c937f87f 100644
> > --- a/net/ipv6/ip6_input.c
> > +++ b/net/ipv6/ip6_input.c
> > @@ -150,6 +150,7 @@ static struct sk_buff *ip6_rcv_core(struct sk_buff *skb, struct net_device *dev,
> >       struct inet6_dev *idev;
> >
> >       if (skb->pkt_type == PACKET_OTHERHOST) {
> > +             atomic_long_inc(&skb->dev->rx_otherhost_dropped);
> >               kfree_skb(skb);
> >               return NULL;
> >       }
>
> that's an expensive packet counter for a common path (e.g., hosting
> environments).

This was the reason for the initial patch, using SNMP stat, being per cpu.

Adding per-device per-cpu data for this counter will increase cost of
netdevice dismantle phase,
and increase time for ndo_get_stats64(), especially on hosts with 256
or 512 cpus.