2e719cca66
Right now to encode per-CPU variables in BTF, pahole iterates complete vmlinux
symbol table for each CU. There are 2500 CUs for a typical kernel image.
Overall, to encode 287 per-CPU variables pahole spends more than 10% of its CPU
budget, this is incredibly wasteful.
This patch revamps how this is done. Now it pre-processes symbol table once
before any of per-CU processing starts. It remembers each per-CPU variable
symbol, including its address, size, and name. Then during processing each CU,
binary search is used to correlate DWARF variable with per-CPU symbols and
figure out if variable belongs to per-CPU data section. If the match is found,
BTF_KIND_VAR is emitted and var_secinfo is recorded, just like before. At the
very end, after all CUs are processed, BTF_KIND_DATASEC is emitted with sorted
variables.
This change makes per-CPU variables generation overhead pretty negligible and
returns back about 10% of CPU usage.
Performance counter stats for './pahole -J /home/andriin/linux-build/default/vmlinux':
BEFORE:
19.160149000 seconds user
1.304873000 seconds sys
24,114.05 msec task-clock # 0.999 CPUs utilized
83 context-switches # 0.003 K/sec
0 cpu-migrations # 0.000 K/sec
622,417 page-faults # 0.026 M/sec
72,897,315,125 cycles # 3.023 GHz (25.02%)
127,807,316,959 instructions # 1.75 insn per cycle (25.01%)
29,087,179,117 branches # 1206.234 M/sec (25.01%)
464,105,921 branch-misses # 1.60% of all branches (25.01%)
30,252,119,368 L1-dcache-loads # 1254.543 M/sec (25.01%)
1,156,336,207 L1-dcache-load-misses # 3.82% of all L1-dcache hits (25.05%)
343,373,503 LLC-loads # 14.240 M/sec (25.02%)
12,044,977 LLC-load-misses # 3.51% of all LL-cache hits (25.01%)
24.136198321 seconds time elapsed
22.729693000 seconds user
1.384859000 seconds sys
AFTER:
16.781455000 seconds user
1.343956000 seconds sys
23,398.77 msec task-clock # 1.000 CPUs utilized
86 context-switches # 0.004 K/sec
0 cpu-migrations # 0.000 K/sec
622,420 page-faults # 0.027 M/sec
68,395,641,468 cycles # 2.923 GHz (25.05%)
114,241,327,034 instructions # 1.67 insn per cycle (25.01%)
26,330,711,718 branches # 1125.303 M/sec (25.01%)
465,926,869 branch-misses # 1.77% of all branches (25.00%)
24,662,984,772 L1-dcache-loads # 1054.029 M/sec (25.00%)
1,054,052,064 L1-dcache-load-misses # 4.27% of all L1-dcache hits (25.00%)
340,970,622 LLC-loads # 14.572 M/sec (25.00%)
16,032,297 LLC-load-misses # 4.70% of all LL-cache hits (25.03%)
23.402259654 seconds time elapsed
21.916437000 seconds user
1.482826000 seconds sys
Committer testing:
$ grep 'model name' -m1 /proc/cpuinfo
model name : AMD Ryzen 9 3900X 12-Core Processor
$
Before:
$ perf stat -r5 pahole -J vmlinux
Performance counter stats for 'pahole -J vmlinux' (5 runs):
9,730.28 msec task-clock:u # 0.998 CPUs utilized ( +- 0.54% )
0 context-switches:u # 0.000 K/sec
0 cpu-migrations:u # 0.000 K/sec
353,854 page-faults:u # 0.036 M/sec ( +- 0.00% )
39,721,726,459 cycles:u # 4.082 GHz ( +- 0.07% ) (83.33%)
626,010,654 stalled-cycles-frontend:u # 1.58% frontend cycles idle ( +- 0.91% ) (83.33%)
7,518,333,691 stalled-cycles-backend:u # 18.93% backend cycles idle ( +- 0.56% ) (83.33%)
85,477,123,093 instructions:u # 2.15 insn per cycle
# 0.09 stalled cycles per insn ( +- 0.02% ) (83.34%)
19,346,085,683 branches:u # 1988.235 M/sec ( +- 0.03% ) (83.34%)
237,291,787 branch-misses:u # 1.23% of all branches ( +- 0.15% ) (83.33%)
9.7465 +- 0.0524 seconds time elapsed ( +- 0.54% )
$
After:
$ perf stat -r5 pahole -J vmlinux
Performance counter stats for 'pahole -J vmlinux' (5 runs):
8,953.80 msec task-clock:u # 0.998 CPUs utilized ( +- 0.09% )
0 context-switches:u # 0.000 K/sec
0 cpu-migrations:u # 0.000 K/sec
353,855 page-faults:u # 0.040 M/sec ( +- 0.00% )
35,775,730,539 cycles:u # 3.996 GHz ( +- 0.07% ) (83.33%)
579,534,836 stalled-cycles-frontend:u # 1.62% frontend cycles idle ( +- 2.21% ) (83.33%)
5,719,840,144 stalled-cycles-backend:u # 15.99% backend cycles idle ( +- 0.93% ) (83.33%)
73,035,744,786 instructions:u # 2.04 insn per cycle
# 0.08 stalled cycles per insn ( +- 0.02% ) (83.34%)
16,798,017,844 branches:u # 1876.077 M/sec ( +- 0.05% ) (83.33%)
237,777,143 branch-misses:u # 1.42% of all branches ( +- 0.15% ) (83.34%)
8.97077 +- 0.00803 seconds time elapsed ( +- 0.09% )
$
Indeed, about 10% shaved, not bad.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Hao Luo <haoluo@google.com>
Cc: Oleg Rombakh <olegrom@google.com>
Cc: bpf@vger.kernel.org
Cc: dwarves@vger.kernel.org
Cc: kernel-team@fb.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
70 lines
2.2 KiB
C
70 lines
2.2 KiB
C
/*
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SPDX-License-Identifier: GPL-2.0-only
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Copyright (C) 2019 Facebook
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*/
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#ifndef _LIBBTF_H
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#define _LIBBTF_H
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#include "gobuffer.h"
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#include <stdbool.h>
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#include <stdint.h>
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#include "lib/bpf/src/btf.h"
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struct btf_elf {
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void *priv;
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Elf *elf;
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GElf_Ehdr ehdr;
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struct elf_symtab *symtab;
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struct gobuffer percpu_secinfo;
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char *filename;
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int in_fd;
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uint8_t wordsize;
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bool is_big_endian;
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bool raw_btf; // "/sys/kernel/btf/vmlinux"
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uint32_t percpu_shndx;
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uint64_t percpu_base_addr;
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struct btf *btf;
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};
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extern uint8_t btf_elf__verbose;
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extern uint8_t btf_elf__force;
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#define btf_elf__verbose_log(fmt, ...) { if (btf_elf__verbose) printf(fmt, __VA_ARGS__); }
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#define PERCPU_SECTION ".data..percpu"
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struct cu;
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struct base_type;
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struct ftype;
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struct btf_elf *btf_elf__new(const char *filename, Elf *elf);
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void btf_elf__delete(struct btf_elf *btf);
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int32_t btf_elf__add_base_type(struct btf_elf *btf, const struct base_type *bt,
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const char *name);
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int32_t btf_elf__add_ref_type(struct btf_elf *btf, uint16_t kind, uint32_t type,
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const char *name, bool kind_flag);
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int btf_elf__add_member(struct btf_elf *btf, const char *name, uint32_t type,
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uint32_t bitfield_size, uint32_t bit_offset);
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int32_t btf_elf__add_struct(struct btf_elf *btf, uint8_t kind, const char *name, uint32_t size);
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int32_t btf_elf__add_array(struct btf_elf *btf, uint32_t type, uint32_t index_type,
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uint32_t nelems);
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int32_t btf_elf__add_enum(struct btf_elf *btf, const char *name, uint32_t size);
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int btf_elf__add_enum_val(struct btf_elf *btf, const char *name, int32_t value);
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int32_t btf_elf__add_func_proto(struct btf_elf *btf, struct cu *cu, struct ftype *ftype,
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uint32_t type_id_off);
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int32_t btf_elf__add_var_type(struct btf_elf *btfe, uint32_t type, const char *name,
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uint32_t linkage);
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int32_t btf_elf__add_var_secinfo(struct gobuffer *buf, uint32_t type,
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uint32_t offset, uint32_t size);
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int32_t btf_elf__add_datasec_type(struct btf_elf *btfe, const char *section_name,
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struct gobuffer *var_secinfo_buf);
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int btf_elf__encode(struct btf_elf *btf, uint8_t flags);
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const char *btf_elf__string(struct btf_elf *btf, uint32_t ref);
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int btf_elf__load(struct btf_elf *btf);
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#endif /* _LIBBTF_H */
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