On Sat, 2024-06-08 at 07:08 -0700, Donglin Peng wrote: [...] > Changes in RFC v3: > - Sort the btf types during the build process in order to reduce memory usage > and decrease boot time. > > RFC v2: > - https://lore.kernel.org/all/20230909091646.420163-1-pengdonglin@xxxxxxxxxxxxxx > --- > include/linux/btf.h | 1 + > kernel/bpf/btf.c | 160 +++++++++++++++++++++++++++++++++--- I think that kernel part is in a good shape, please split it as a separate commit. > tools/lib/bpf/btf.c | 195 ++++++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 345 insertions(+), 11 deletions(-) [...] > diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c > index 2d0840ef599a..93c1ab677bfa 100644 I'm not sure that libbpf is the best place to put this functionality, as there might be different kinds of orderings (e.g. see a fresh commit to bpftool to output stable vmlinux.h: 94133cf24bb3 "bpftool: Introduce btf c dump sorting"). I'm curious what Andrii, Alan and Arnaldo think on libbpf vs pahole for this feature. Also, I have a selftests build failure with this patch-set (and I suspect that a bunch of dedup test cases would need an update): $ pwd /home/eddy/work/bpf-next/tools/testing/selftests/bpf $ make -j14 test_progs ... GEN-SKEL [test_progs] access_map_in_map.skel.h Binary files /home/eddy/work/bpf-next/tools/testing/selftests/bpf/access_map_in_map.bpf.linked2.o and /home/eddy/work/bpf-next/tools/testing/selftests/bpf/access_map_in_map.bpf.linked3.o differ make: *** [Makefile:658: /home/eddy/work/bpf-next/tools/testing/selftests/bpf/access_map_in_map.skel.h] Error 1 make: *** Waiting for unfinished jobs.... If this change remains in libbpf, I think it would be great to update btf_find_by_name_kind() to work the same way as kernel one. > --- a/tools/lib/bpf/btf.c > +++ b/tools/lib/bpf/btf.c [...] > +static int btf_sort_type_by_name(struct btf *btf) > +{ > + struct btf_type *bt; > + __u32 *new_type_offs = NULL, *new_type_offs_noname = NULL; > + __u32 *maps = NULL, *found_offs; > + void *new_types_data = NULL, *loc_data; > + int i, j, k, type_cnt, ret = 0, type_size; > + __u32 data_size; > + > + if (btf_ensure_modifiable(btf)) > + return libbpf_err(-ENOMEM); > + > + type_cnt = btf->nr_types; > + data_size = btf->type_offs_cap * sizeof(*new_type_offs); > + > + maps = (__u32 *)malloc(type_cnt * sizeof(__u32)); > + if (!maps) { > + ret = -ENOMEM; > + goto err_out; > + } > + > + new_type_offs = (__u32 *)malloc(data_size); > + if (!new_type_offs) { > + ret = -ENOMEM; > + goto err_out; > + } > + > + new_type_offs_noname = (__u32 *)malloc(data_size); > + if (!new_type_offs_noname) { > + ret = -ENOMEM; > + goto err_out; > + } What is the point of separating offsets in new_type_offs vs new_type_offs_noname? It should be possible to use a single offsets array and have a comparison function that puts all named types before unnamed. > + > + new_types_data = malloc(btf->types_data_cap); > + if (!new_types_data) { > + ret = -ENOMEM; > + goto err_out; > + } > + > + memset(new_type_offs, 0, data_size); > + > + for (i = 0, j = 0, k = 0; i < type_cnt; i++) { > + const char *name; > + > + bt = (struct btf_type *)(btf->types_data + btf->type_offs[i]); > + name = btf__str_by_offset(btf, bt->name_off); > + if (!name || !name[0]) > + new_type_offs_noname[k++] = btf->type_offs[i]; > + else > + new_type_offs[j++] = btf->type_offs[i]; > + } > + > + memmove(new_type_offs + j, new_type_offs_noname, sizeof(__u32) * k); > + > + qsort_r(new_type_offs, j, sizeof(*new_type_offs), > + btf_compare_type_name, btf); > + > + for (i = 0; i < type_cnt; i++) { > + found_offs = bsearch(&new_type_offs[i], btf->type_offs, type_cnt, > + sizeof(__u32), btf_compare_offs); > + if (!found_offs) { > + ret = -EINVAL; > + goto err_out; > + } > + maps[found_offs - btf->type_offs] = i; > + } > + > + loc_data = new_types_data; > + for (i = 0; i < type_cnt; i++, loc_data += type_size) { > + bt = (struct btf_type *)(btf->types_data + new_type_offs[i]); > + type_size = btf_type_size(bt); > + if (type_size < 0) { > + ret = type_size; > + goto err_out; > + } > + > + memcpy(loc_data, bt, type_size); > + > + bt = (struct btf_type *)loc_data; > + switch (btf_kind(bt)) { Please take a look at btf_dedup_remap_types(): it uses newly added iterator interface to enumerate all ID references in the type. It could be used here to avoid enumerating every BTF kind. Also, the d->hypot_map could be used instead of `maps`. And if so, I think that it should be possible to put this pass before btf_dedup_remap_types() in order for it to do the remapping. Alternatively, it might make sense to merge this pass with btf_dedup_compact_types() in order to minimize number of operations, e.g. as in my crude attempt: https://github.com/eddyz87/bpf/tree/binsort-btf-dedup (fails with similar selftests issue). > + case BTF_KIND_PTR: > + case BTF_KIND_CONST: > + case BTF_KIND_VOLATILE: > + case BTF_KIND_RESTRICT: > + case BTF_KIND_TYPEDEF: > + case BTF_KIND_TYPE_TAG: > + case BTF_KIND_FUNC: > + case BTF_KIND_VAR: > + case BTF_KIND_DECL_TAG: > + bt->type = btf_get_mapped_type(btf, maps, bt->type); > + break; [...]
