Messages in this thread | | | Date | Thu, 10 Jun 2021 13:59:28 -0700 | From | Nathan Chancellor <> | Subject | Re: [PATCH 01/13] objtool: Rewrite hashtable sizing |
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On Thu, Jun 10, 2021 at 09:33:44PM +0200, Peter Zijlstra wrote: > On Thu, Jun 10, 2021 at 11:50:36AM -0700, Sami Tolvanen wrote: > > On Thu, Jun 10, 2021 at 11:14 AM Nathan Chancellor <nathan@kernel.org> wrote: > > > Adding Sami because I am not sure why this patch would have much of an impact > > > in relation to LTO. https://git.kernel.org/tip/25cf0d8aa2a3 is the patch in > > > question. > > > > It's because LLVM enables -ffunction-sections with LTO, so using .text > > section size to estimate the reloc hash table size isn't going to be > > accurate, as confirmed by objtool output with --stats: > > > > OBJTOOL vmlinux.o > > nr_sections: 141481 > > section_bits: 17 > > nr_symbols: 215262 > > symbol_bits: 17 > > max_reloc: 24850 > > tot_reloc: 590890 > > reloc_bits: 10 > > Bah. Would something like the *completely* untested below help with that?
LGTM, thanks for the quick fix!
Benchmark #1: allmodconfig Time (mean ± σ): 624.555 s ± 2.089 s [User: 35109.967 s, System: 2146.215 s] Range (min … max): 623.078 s … 626.032 s 2 runs
Benchmark #2: allmodconfig with ThinLTO Time (mean ± σ): 769.959 s ± 1.819 s [User: 39692.409 s, System: 2308.010 s] Range (min … max): 768.673 s … 771.245 s 2 runs
Summary 'allmodconfig' ran 1.23 ± 0.01 times faster than 'allmodconfig with ThinLTO'
Tested-by: Nathan Chancellor <nathan@kernel.org>
> --- > diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c > index 25f6d293bc86..8676c7598728 100644 > --- a/tools/objtool/elf.c > +++ b/tools/objtool/elf.c > @@ -288,6 +288,9 @@ static int read_sections(struct elf *elf) > } > sec->len = sec->sh.sh_size; > > + if (sec->sh.sh_flags & SHF_EXECINSTR) > + elf->text_size += sec->len; > + > list_add_tail(&sec->list, &elf->sections); > elf_hash_add(section, &sec->hash, sec->idx); > elf_hash_add(section_name, &sec->name_hash, str_hash(sec->name)); > @@ -581,13 +584,7 @@ static int read_relocs(struct elf *elf) > unsigned int symndx; > unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0; > > - sec = find_section_by_name(elf, ".text"); > - if (!sec) { > - WARN("no .text"); > - return -1; > - } > - > - if (!elf_alloc_hash(reloc, sec->len / 16)) > + if (!elf_alloc_hash(reloc, elf->text_size / 16)) > return -1; > > list_for_each_entry(sec, &elf->sections, list) { > diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h > index 90082751f851..e34395047530 100644 > --- a/tools/objtool/include/objtool/elf.h > +++ b/tools/objtool/include/objtool/elf.h > @@ -83,6 +83,7 @@ struct elf { > int fd; > bool changed; > char *name; > + unsigned int text_size; > struct list_head sections; > > int symbol_bits;
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