On Thu, 21 Feb 2019 12:56:54 +0100, Toke Høiland-Jørgensen wrote:
> A common pattern when using xdp_redirect_map() is to create a device map
> where the lookup key is simply ifindex. Because device maps are arrays,
> this leaves holes in the map, and the map has to be sized to fit the
> largest ifindex, regardless of how many devices actually are actually
> needed in the map.
>
> This patch adds a second type of device map where the key is interpreted as
> an ifindex and looked up using a hashmap, instead of being used as an array
> index. This leads to maps being densely packed, so they can be smaller.
>
> The default maps used by xdp_redirect() are changed to use the new map
> type, which means that xdp_redirect() is no longer limited to ifindex < 64,
> but instead to 64 total simultaneous interfaces per network namespace. This
> also provides an easy way to compare the performance of devmap and
> devmap_idx:
>
> xdp_redirect_map (devmap): 8394560 pkt/s
> xdp_redirect (devmap_idx): 8179480 pkt/s
>
> Difference: 215080 pkt/s or 3.1 nanoseconds per packet.
Could you share what the ifindex mix was here, to arrive at these
numbers? How does it compare to using an array but not keying with
ifindex?
> Signed-off-by: Toke Høiland-Jørgensen <t...@redhat.com>
> +static int dev_map_idx_update_elem(struct bpf_map *map, void *key, void
> *value,
> + u64 map_flags)
> +{
> + struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
> + struct bpf_dtab_netdev *dev, *old_dev;
> + u32 idx = *(u32 *)key;
> + u32 val = *(u32 *)value;
> + u32 bit;
> +
> + if (unlikely(map_flags > BPF_EXIST))
> + return -EINVAL;
> + if (unlikely(map_flags == BPF_NOEXIST))
> + return -EEXIST;
> +
> + old_dev = __dev_map_idx_lookup_elem(map, idx);
> + if (!val) {
> + if (!old_dev)
> + return 0;
IMHO this is a fairly strange mix of array and hashmap semantics. I
think you should stick to hashmap behaviour AFA flags and update/delete
goes.
> + xchg(&dtab->netdev_map[old_dev->bit], NULL);
> + spin_lock(&dtab->index_lock);
> + hlist_del_rcu(&old_dev->index_hlist);
> + spin_unlock(&dtab->index_lock);
> +
> + clear_bit_unlock(old_dev->bit, dtab->bits_used);
> + call_rcu(&old_dev->rcu, __dev_map_entry_free);
> + } else {
> + if (idx != val)
> + return -EINVAL;
> + if (old_dev)
> + return 0;
> + if (!__dev_map_find_bit(dtab, &bit))
> + return -E2BIG;
> + dev = __dev_map_alloc_node(dtab, idx, bit);
> + if (IS_ERR(dev))
> + return PTR_ERR(dev);
> +
> + xchg(&dtab->netdev_map[bit], dev);
> + spin_lock(&dtab->index_lock);
> + hlist_add_head_rcu(&dev->index_hlist,
> + dev_map_index_hash(dtab, dev->ifindex));
> + spin_unlock(&dtab->index_lock);
> + }
> + return 0;
> +}
> +
> const struct bpf_map_ops dev_map_ops = {
> .map_alloc = dev_map_alloc,
> .map_free = dev_map_free,
