I have two port running xdp prog. Each have same type, struct and purpose maps. I want to use shared map. So tested such a way, run xdp prog on each device with only one func - bpf_tail_call. This calls to the third xdp prog and gets and saves data to its maps. So is it only such a way, or may be another way? 
If only one, how can i control, that bpf_tail_call not drop some packets?
And what "cost" have bpf_tail_call? Is it cheap or not? Or its better to send to main(third) prog to save data in man not xdp_md , but may by some (8 bytes) needed to save data?