A backlog queue is used to buffer incoming traffic and its length is controlled by net.core.netdev_max_backlog. On fast connections (10Gb/s or higher) the default backlog length of 1024 can be insufficient; here the backlog length is increased if 1/16 of current backlog size in the last minute is dropped (drops occur when the backlog limit is reached). In addition, backlog drops can avoid small flows; the tunable net.core.flow_limit_cpu_bitmap can be used to set this on a per-cpu basis; when we see sufficient drops on a CPU, the appropriate bit is set in the CPU bitmask to prioritize small flows for drop avoidance.

Tunables:

bpf(2), bpftune(8),