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Message-ID: <Z8tbEgh7rZscggv6@x1>
Date: Fri, 7 Mar 2025 17:46:10 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Stephen Brennan <stephen.s.brennan@...cle.com>,
Namhyung Kim <namhyung@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
"Liang, Kan" <kan.liang@...ux.intel.com>,
Mark Rutland <mark.rutland@....com>,
Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
James Clark <james.clark@...aro.org>,
Chaitanya S Prakash <chaitanyas.prakash@....com>,
Ian Rogers <irogers@...gle.com>, linux-perf-users@...r.kernel.org,
Adrian Hunter <adrian.hunter@...el.com>,
Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v2 0/3] Support .gnu_debugdata for symbols in perf
On Fri, Mar 07, 2025 at 05:18:36PM -0300, Arnaldo Carvalho de Melo wrote:
> The NO_LZMA code in the perf build system should at this point either be
> deleted, as elfutils is so critical for perf, or mean that outside of
> elfutils, perf should make no use of lzma, which seems odd even with
> some potentially marginal value.
> So for testing this series I'll have to collect data before these
> patches get applied, making sure we collect samples from symbols in
> binaries with a MiniDebuginfo section, do a perf report, see them as
> being not resolved after making sure we don't have its debuginfo files
> installed and zapping whatever local debuginfo cache we have
> (debuginfod, perfs, etc), apply the patches and then see if it gets more
> symbols resolved by looking at the .gnu_debugdata section.
>
> Ok, doing that now.
Works:
⬢ [acme@...lbox perf-tools-next]$ taskset -c 0 perf record -e cpu_core/cycles/P find . > /dev/null
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.011 MB perf.data (163 samples) ]
⬢ [acme@...lbox perf-tools-next]$ perf report --stdio > before
⬢ [acme@...lbox perf-tools-next]$
Apply the patches and:
⬢ [acme@...lbox perf-tools-next]$ perf report --stdio > after
⬢ [acme@...lbox perf-tools-next]$ diff -u before after
--- before 2025-03-07 17:33:15.113447391 -0300
+++ after 2025-03-07 17:33:39.291525994 -0300
@@ -9,88 +9,56 @@
# Overhead Command Shared Object Symbol
# ........ ....... .................... ..................................
#
+ 8.72% find find [.] consider_visiting
7.90% find libc.so.6 [.] __GI___readdir64
7.44% find libc.so.6 [.] _int_malloc
+ 7.06% find find [.] find
+ 6.20% find find [.] fts_build.constprop.0
6.18% find libc.so.6 [.] __memmove_avx_unaligned_erms
+ 4.36% find find [.] pred_print
4.14% find libc.so.6 [.] __printf_buffer
3.65% find libc.so.6 [.] __strlen_avx2
3.35% find libc.so.6 [.] malloc
- 2.65% find find [.] 0x000000000000b498
+ 2.85% find find [.] fts_alloc
2.51% find libc.so.6 [.] __vfprintf_internal
2.45% find libc.so.6 [.] __fprintf_chk
- 2.45% find find [.] 0x00000000000089e3
2.33% find libc.so.6 [.] __printf_buffer_write
2.13% find libc.so.6 [.] _int_free_merge_chunk
1.88% find libc.so.6 [.] __printf_buffer_flush_to_file
- 1.87% find find [.] 0x000000000000bf8e
1.79% find libc.so.6 [.] _int_free
1.64% find libc.so.6 [.] msort_with_tmp.part.0
1.63% find find [.] free@plt
- 1.34% find find [.] 0x000000000000c214
- 1.30% find find [.] 0x000000000001ea34
- 1.27% find find [.] 0x000000000001ea96
+ 1.29% find find [.] fts_safe_changedir.lto_priv.0
1.26% find [unknown] [k] 0xffffffffad4001c8
1.25% find libc.so.6 [.] __libc_fcntl64
1.23% find libc.so.6 [.] _int_free_create_chunk
- 1.22% find find [.] 0x000000000000bfb9
- 1.22% find find [.] 0x000000000000bbde
- 1.22% find find [.] 0x000000000000b4a2
- 1.20% find find [.] 0x0000000000006918
+ 1.20% find find [.] pred_and
1.16% find libc.so.6 [.] __fcntl64_nocancel_adjusted
+ 1.15% find find [.] AD_hash
1.12% find libc.so.6 [.] cfree@...BC_2.2.5
1.05% find libc.so.6 [.] __strchrnul_ifunc@plt
1.03% find libc.so.6 [.] __libc_openat64
1.01% find libc.so.6 [.] __strchrnul_avx2
- 0.69% find find [.] 0x0000000000008a0e
- 0.68% find find [.] 0x000000000000b553
- 0.67% find find [.] 0x000000000001ea63
- 0.67% find find [.] 0x0000000000006869
- 0.65% find find [.] 0x0000000000019e82
- 0.65% find find [.] 0x000000000000bbc5
- 0.65% find find [.] 0x000000000001117e
- 0.64% find find [.] 0x0000000000019fc6
- 0.64% find find [.] 0x000000000001111c
- 0.63% find find [.] 0x0000000000008a19
- 0.63% find find [.] 0x0000000000018b3d
- 0.63% find find [.] 0x000000000000b61e
+ 0.97% find find [.] leave_dir.lto_priv.0
+ 0.67% find find [.] apply_predicate
+ 0.63% find find [.] cwd_advance_fd.lto_priv.0
0.63% find libc.so.6 [.] __GI___fstatat64
- 0.63% find find [.] 0x000000000001f0de
0.63% find libc.so.6 [.] __fstat64
- 0.63% find find [.] 0x000000000001edfb
- 0.62% find find [.] 0x000000000001113f
- 0.61% find find [.] 0x000000000000c223
- 0.61% find find [.] 0x000000000000c06b
- 0.61% find find [.] 0x000000000000fd90
- 0.61% find find [.] 0x0000000000018d98
- 0.60% find find [.] 0x0000000000017cfa
- 0.60% find find [.] 0x000000000001e990
- 0.60% find find [.] 0x000000000000b657
+ 0.60% find find [.] rpl_fcntl
0.59% find find [.] malloc@plt
- 0.59% find find [.] 0x000000000000c099
- 0.59% find find [.] 0x00000000000089d9
0.58% find ld-linux-x86-64.so.2 [.] _dl_process_pt_gnu_property
0.57% find libc.so.6 [.] unlink_chunk.isra.0
- 0.56% find find [.] 0x000000000001ea4e
- 0.56% find find [.] 0x000000000000b64b
0.56% find libc.so.6 [.] malloc@plt
- 0.54% find find [.] 0x00000000000110e6
- 0.54% find find [.] 0x000000000001ead0
- 0.54% find find [.] 0x000000000000fdc7
- 0.53% find find [.] 0x000000000000fd8a
- 0.52% find find [.] 0x0000000000011e07
- 0.52% find find [.] 0x000000000000b6a8
- 0.48% find find [.] 0x0000000000012463
+ 0.54% find find [.] fts_compare_ino
+ 0.52% find find [.] hash_find_entry
+ 0.48% find find [.] fts_sort
0.47% find libc.so.6 [.] __printf_buffer_to_file_switch
0.42% find libc.so.6 [.] alloc_perturb
- 0.42% find find [.] 0x000000000000bfc2
- 0.41% find find [.] 0x0000000000011179
- 0.40% find find [.] 0x000000000000c234
- 0.36% find find [.] 0x0000000000018cc0
0.14% find ld-linux-x86-64.so.2 [.] _dl_sysdep_parse_arguments
0.01% find ld-linux-x86-64.so.2 [.] _dl_start
0.00% find ld-linux-x86-64.so.2 [.] _start
#
-# (Tip: Create an archive with symtabs to analyse on other machine: perf archive)
+# (Tip: To see callchains in a more compact form: perf report -g folded)
#
⬢ [acme@...lbox perf-tools-next]$
⬢ [acme@...lbox perf-tools-next]$ find ~/.debug/ -name af3f04d1b31abc9e5ce8428110e424fd980a37
⬢ [acme@...lbox perf-tools-next]$ find ~/.cache/ -name af3f04d1b31abc9e5ce8428110e424fd980a37
⬢ [acme@...lbox perf-tools-next]$
⬢ [acme@...lbox perf-tools-next]$ rpm -qf /bin/find
findutils-4.9.0-9.fc40.x86_64
⬢ [acme@...lbox perf-tools-next]$ rpm -q findutils-debuginfo
package findutils-debuginfo is not installed
⬢ [acme@...lbox perf-tools-next]$
And /bin/find has only unresolved symbols in its symtabs:
⬢ [acme@...lbox perf-tools-next]$ readelf -sW /bin/find | grep -w FUNC | wc -l
145
⬢ [acme@...lbox perf-tools-next]$ readelf -sW /bin/find | grep -w FUNC | grep -vw UND
⬢ [acme@...lbox perf-tools-next]$
⬢ [acme@...lbox perf-tools-next]$ readelf -SW /bin/find | grep SYM
[ 7] .dynsym DYNSYM 00000000000004a0 0004a0 000ed0 18 A 8 1 8
[ 9] .gnu.version VERSYM 00000000000019a0 0019a0 00013c 02 A 7 0 2
⬢ [acme@...lbox perf-tools-next]$
And that matches eu-readelf output, almost the same (UND => UNDEF):
⬢ [acme@...lbox perf-tools-next]$ eu-readelf -s /bin/find | grep -w FUNC | wc -l
145
⬢ [acme@...lbox perf-tools-next]$
⬢ [acme@...lbox perf-tools-next]$ eu-readelf -s /bin/find | grep -w FUNC | grep -vw UNDEF
⬢ [acme@...lbox perf-tools-next]$
It has a way to use that section tho:
⬢ [acme@...lbox perf-tools-next]$ man eu-readelf | grep -A2 -- --elf-section
[--elf-section [section] ]
[-w|
--debug-dump[=line,=decodedline,=info,=info+,=abbrev,=pubnames,=aranges,=macro,=frames,=str,=loc,=ranges,=gdb_index,=addr]]
--
--elf-section [section]
Use the named SECTION (default .gnu_debugdata) as (compressed) ELF input data
⬢ [acme@...lbox perf-tools-next]$
⬢ [acme@...lbox perf-tools-next]$ eu-readelf --elf-section -s /bin/find | grep -w FUNC | grep -vw UNDEF | wc -l
339
⬢ [acme@...lbox perf-tools-next]$ eu-readelf --elf-section -s /bin/find | grep -w FUNC | grep -vw UNDEF | head
1: 00000000000056d0 35 FUNC LOCAL DEFAULT 17 entry_hashfunc
2: 0000000000005700 34 FUNC LOCAL DEFAULT 17 entry_comparator
3: 0000000000005920 121 FUNC LOCAL DEFAULT 17 subtree_has_side_effects
4: 00000000000059a0 992 FUNC LOCAL DEFAULT 17 worst_cost.part.0
5: 0000000000005d80 449 FUNC LOCAL DEFAULT 17 traverse_tree
6: 0000000000005f50 73 FUNC LOCAL DEFAULT 17 undangle_file_pointers
7: 0000000000005fa0 72 FUNC LOCAL DEFAULT 17 looks_like_expression
8: 0000000000006030 303 FUNC LOCAL DEFAULT 17 get_fts_info_name
9: 0000000000006190 35 FUNC LOCAL DEFAULT 17 inside_dir.part.0
10: 0000000000006330 451 FUNC LOCAL DEFAULT 17 pred_sanity_check
⬢ [acme@...lbox perf-tools-next]$
So there we can find the new entries, such as the top one in the example
profile session above:
⬢ [acme@...lbox perf-tools-next]$ eu-readelf --elf-section -s /bin/find | grep -w FUNC | grep -vw UNDEF | grep -w consider_visiting
48: 000000000000b460 2544 FUNC LOCAL DEFAULT 17 consider_visiting
⬢ [acme@...lbox perf-tools-next]$
And trat address matches the resolution perf did with your patches:
⬢ [acme@...lbox perf-tools-next]$ perf report -v --stdio |& head
build id event received for [vdso]: a2184b81fbbc08eff401d16259eca8ad5f9d8988 [20]
build id event received for /usr/bin/find: 3faf3f04d1b31abc9e5ce8428110e424fd980a37 [20]
build id event received for /usr/lib64/ld-linux-x86-64.so.2: 765f7ab0f3569ffe98de85864a0cedda9b686994 [20]
build id event received for /usr/lib64/libc.so.6: c8c3fa52aaee3f5d73b6fd862e39e9d4c010b6ba [20]
build id event received for [kernel.kallsyms]: c3fbb7df4dfb94762b1648bc65e4363e50f45585 [20]
read_gnu_debugdata: using .gnu_debugdata of /usr/bin/find
# To display the perf.data header info, please use --header/--header-only options.
#
#
# Total Lost Samples: 0
⬢ [acme@...lbox perf-tools-next]$ perf report -v --stdio |& head -20
build id event received for [vdso]: a2184b81fbbc08eff401d16259eca8ad5f9d8988 [20]
build id event received for /usr/bin/find: 3faf3f04d1b31abc9e5ce8428110e424fd980a37 [20]
build id event received for /usr/lib64/ld-linux-x86-64.so.2: 765f7ab0f3569ffe98de85864a0cedda9b686994 [20]
build id event received for /usr/lib64/libc.so.6: c8c3fa52aaee3f5d73b6fd862e39e9d4c010b6ba [20]
build id event received for [kernel.kallsyms]: c3fbb7df4dfb94762b1648bc65e4363e50f45585 [20]
read_gnu_debugdata: using .gnu_debugdata of /usr/bin/find
# To display the perf.data header info, please use --header/--header-only options.
#
#
# Total Lost Samples: 0
#
# Samples: 163 of event 'cpu_core/cycles/Pu'
# Event count (approx.): 68126524
#
# Overhead Command Shared Object Symbol
# ........ ....... ............................... .......................................................
#
8.72% find /usr/bin/find 0xb498
7.90% find /usr/lib64/libc.so.6 0xe51e0 B [.] __GI___readdir64
7.44% find /usr/lib64/libc.so.6 0xa77cd B [.] _int_malloc
⬢ [acme@...lbox perf-tools-next]$
The only strange thing was not having it resolved in the -v case, which
I think its because you added a new type of DSO but didn't update the
code that does the 'perf report -v' verbose case?
I ran out of time, have to go AFK now, can you please take a look,
Stephen?
DSO_BINARY_TYPE__GNU_DEBUGDATA should be handled at...
int dso__read_binary_type_filename(const struct dso *dso,
enum dso_binary_type type,
char *root_dir, char *filename, size_t size)
But you have it there, ok, I'll try to continue later.
Other than that the patch looks great and makes use of this new mini
symtab, excellent!
- Arnaldo
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