On 1/26/21 10:39 AM, Jesper Dangaard Brouer wrote: > The current layout of net_device is not optimal for cacheline usage. > > The member adj_list.lower linked list is split between cacheline 2 and 3. > The ifindex is placed together with stats (struct net_device_stats), > although most modern drivers don't update this stats member. > > The members netdev_ops, mtu and hard_header_len are placed on three > different cachelines. These members are accessed for XDP redirect into > devmap, which were noticeably with perf tool. When not using the map > redirect variant (like TC-BPF does), then ifindex is also used, which is > placed on a separate fourth cacheline. These members are also accessed > during forwarding with regular network stack. The members priv_flags and > flags are on fast-path for network stack transmit path in __dev_queue_xmit > (currently located together with mtu cacheline). > > This patch creates a read mostly cacheline, with the purpose of keeping the > above mentioned members on the same cacheline. > > Some netdev_features_t members also becomes part of this cacheline, which is > on purpose, as function netif_skb_features() is on fast-path via > validate_xmit_skb(). A long over due look at the organization of this struct. Do you have performance numbers for the XDP case?
