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dwarf_loader: Do not look for non-C DWARF attributes in C CUs 

Avoid looking for attributes that doesn't apply to the C language, such
as DW_AT_virtuality (virtual, pure_virtual), DW_AT_accessibility
(public, protected, private) and DW_AT_const_value.

Looking for those attributes in class_member__new() makes
libdw_find_attr() linearly search all attributes for a die, which
appears on profiling.

Before:

  $ perf stat -r5 pahole --btf_encode_detached=vmlinux.btf -j vmlinux

   Performance counter stats for 'pahole --btf_encode_detached=vmlinux.btf -j vmlinux' (5 runs):

           11,239.99 msec task-clock:u              #    2.921 CPUs utilized    ( +-  0.08% )
                   0      context-switches:u        #    0.000 /sec
                   0      cpu-migrations:u          #    0.000 /sec
             793,897      page-faults:u             #   70.631 K/sec            ( +-  0.00% )
      34,593,518,484      cycles:u                  #    3.078 GHz              ( +-  0.05% )
      75,592,805,563      instructions:u            #    2.19  insn per cycle   ( +-  0.00% )
      17,923,046,622      branches:u                #    1.595 G/sec            ( +-  0.00% )
         131,080,371      branch-misses:u           #    0.73% of all branches  ( +-  0.18% )

              3.84794 +- 0.00327 seconds time elapsed  ( +-  0.09% )
  $

After:

  $ perf stat -r5 pahole --btf_encode_detached=vmlinux.btf -j vmlinux

   Performance counter stats for 'pahole --btf_encode_detached=vmlinux.btf -j vmlinux' (5 runs):

           11,178.28 msec task-clock:u              #    2.929 CPUs utilized            ( +-  0.12% )
                   0      context-switches:u        #    0.000 /sec
                   0      cpu-migrations:u          #    0.000 /sec
             793,890      page-faults:u             #   71.021 K/sec                    ( +-  0.00% )
      34,378,886,265      cycles:u                  #    3.076 GHz                      ( +-  0.13% )
      75,523,849,140      instructions:u            #    2.20  insn per cycle           ( +-  0.12% )
      17,907,573,910      branches:u                #    1.602 G/sec                    ( +-  0.12% )
         130,137,529      branch-misses:u           #    0.73% of all branches          ( +-  0.50% )

              3.8165 +- 0.0137 seconds time elapsed  ( +-  0.36% )

  $

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Arnaldo Carvalho de Melo 2021-07-16 17:09:56 -03:00
parent 88265eab35
commit 1ef1639039
1 changed files with 6 additions and 3 deletions
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9
dwarf_loader.c
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@ -860,7 +860,6 @@ static struct class_member *class_member__new(Dwarf_Die *die, struct cu *cu,
if (member != NULL) {
tag__init(&member->tag, cu, die);
member->name = attr_string(die, DW_AT_name, conf);
member->const_value = attr_numeric(die, DW_AT_const_value);
member->alignment = attr_numeric(die, DW_AT_alignment);
Dwarf_Attribute attr;
@ -899,8 +898,12 @@ static struct class_member *class_member__new(Dwarf_Die *die, struct cu *cu,
member->bit_hole = 0;
member->bitfield_end = 0;
member->visited = 0;
member->accessibility = attr_numeric(die, DW_AT_accessibility);
member->virtuality = attr_numeric(die, DW_AT_virtuality);
if (!cu__is_c(cu)) {
member->accessibility = attr_numeric(die, DW_AT_accessibility);
member->const_value = attr_numeric(die, DW_AT_const_value);
member->virtuality = attr_numeric(die, DW_AT_virtuality);
}
member->hole = 0;
}