On 15/06/2024 15:59, Donglin Peng wrote: > On Sat, Jun 15, 2024 at 7:49 PM Donglin Peng <dolinux.peng@xxxxxxxxx> wrote: >> >> On Tue, Jun 11, 2024 at 6:13 PM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote: >>> >>> 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. >> >> Okay, thanks. >> >>> >>>> 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"). >> >> Thanks, I think it would be better to put it into the libbpf. However, I would >> also like to hear the opinions of others. >> >>> >>> 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): > > Yes，many test cases need to be updated as the BTF layout is modified > unconditionally. > If the plan is to fold the sorting into dedup, pahole will inherit it by default I suppose. Would it be worth making sorting optional (or at least providing a way to switch if off) via a dedup_opts option? If we had an on/off switch we could control sorting via a --btf_features option to pahole. One thing we lose with sorting is that currently the base and often-used types tend to cluster at initial BTF ids, so in some cases linear searches find what they're looking for pretty quickly. Would it be worth maintaining a name-sorted index for BTF perhaps? That would mean not changing type id order (so linear search is unaffected), but for btf_find_by_name_kind() searches the index could be used. See the btf_relocate.c code at [1] for an example of this where a name-based sort index is constructed for the smaller distilled base BTF. [1] https://lore.kernel.org/bpf/20240613095014.357981-4-alan.maguire@xxxxxxxxxx/
