On Mon, 28 May 2018 02:43:38 +0200 Daniel Borkmann <dan...@iogearbox.net> wrote:
> While some of the BPF map lookup helpers provide a ->map_gen_lookup() > callback for inlining the map lookup altogether it is not available > for every map, so the remaining ones have to call bpf_map_lookup_elem() > helper which does a dispatch to map->ops->map_lookup_elem(). In > times of retpolines, this will control and trap speculative execution > rather than letting it do its work for the indirect call and will > therefore cause a slowdown. Likewise, bpf_map_update_elem() and > bpf_map_delete_elem() do not have an inlined version and need to call > into their map->ops->map_update_elem() resp. map->ops->map_delete_elem() > handlers. > > Before: > > # bpftool p d x i 1 I would really appreciate if we can use the long options in these kind of examples. It makes the command "self-documenting" and searchable by google. Here it would be: # bpftool prog dump xlated id 1 > 0: (bf) r2 = r10 > 1: (07) r2 += -8 > 2: (7a) *(u64 *)(r2 +0) = 0 > 3: (18) r1 = map[id:1] > 5: (85) call __htab_map_lookup_elem#232656 > 6: (15) if r0 == 0x0 goto pc+4 > 7: (71) r1 = *(u8 *)(r0 +35) > 8: (55) if r1 != 0x0 goto pc+1 > 9: (72) *(u8 *)(r0 +35) = 1 > 10: (07) r0 += 56 > 11: (15) if r0 == 0x0 goto pc+4 > 12: (bf) r2 = r0 > 13: (18) r1 = map[id:1] > 15: (85) call bpf_map_delete_elem#215008 <-- indirect call via > 16: (95) exit helper > > After: > > # bpftool p d x i 1 Same here > 0: (bf) r2 = r10 > 1: (07) r2 += -8 > 2: (7a) *(u64 *)(r2 +0) = 0 > 3: (18) r1 = map[id:1] > 5: (85) call __htab_map_lookup_elem#233328 > 6: (15) if r0 == 0x0 goto pc+4 > 7: (71) r1 = *(u8 *)(r0 +35) > 8: (55) if r1 != 0x0 goto pc+1 > 9: (72) *(u8 *)(r0 +35) = 1 > 10: (07) r0 += 56 > 11: (15) if r0 == 0x0 goto pc+4 > 12: (bf) r2 = r0 > 13: (18) r1 = map[id:1] > 15: (85) call htab_lru_map_delete_elem#238240 <-- direct call > 16: (95) exit > -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
