> >> +static int get_xps_queue(struct net_device *dev, struct sk_buff *skb)
> >> {
> >> #ifdef CONFIG_XPS
> >> struct xps_dev_maps *dev_maps;
> >> - struct xps_map *map;
> >> + struct sock *sk = skb->sk;
> >> int queue_index = -1;
> >>
> >> if (!static_key_false(&xps_needed))
> >> return -1;
> >>
> >> rcu_read_lock();
> >> - dev_maps = rcu_dereference(dev->xps_cpus_map);
> >> + if (!static_key_false(&xps_rxqs_needed))
> >> + goto get_cpus_map;
> >> +
> >> + dev_maps = rcu_dereference(dev->xps_rxqs_map);
> >> if (dev_maps) {
> >> - unsigned int tci = skb->sender_cpu - 1;
> >> + int tci = sk_rx_queue_get(sk);
> >
> > What if the rx device differs from the tx device?
> >
> I think I have 3 options here:
> 1. Cache the ifindex in sock_common which will introduce a new
> additional field in sock_common.
> 2. Use dev_get_by_napi_id to get the device id. This could be expensive,
> if the rxqs_map is set, this will be done on every packet and involves
> walking through the hashlist for napi_id lookup.
The tx queue mapping is cached in the sk for connected sockets, but
indeed this would be expensive for many workloads.
> 3. Remove validating device id, similar to how it is in skb_tx_hash
> where rx_queue recorded is used and if not, fall through to flow hash
> calculation.
> What do you think is suitable here?
Alternatively, just accept the misprediction in this rare case. But do
make the caveat explicit in the documentation.
