It got faster a bit:
#
# Before:
#
$ perf stat --sync --repeat 5 ./git fsck >/dev/null
Performance counter stats for './git fsck' (5 runs):
32011.163574 task-clock # 0.998 CPUs utilized ( +- 0.08% )
46 context-switches # 0.000 M/sec ( +- 2.77% )
0 CPU-migrations # 0.000 M/sec ( +- 0.00% )
60,279 page-faults # 0.002 M/sec ( +- 12.21% )
102,597,312,322 cycles # 3.205 GHz ( +- 0.08% )
27,303,254,781 stalled-cycles # 26.61% of all cycles are idle ( +- 2.51% )
152,359,589,474 instructions # 1.49 insns per cycle
# 0.18 stalled cycles per insn ( +- 0.03% )
13,225,673,730 branches # 413.158 M/sec ( +- 0.06% )
1,226,749,384 branch-misses # 9.28% of all branches ( +- 0.08% ) 32.083499222 seconds time elapsed ( +- 0.07% )
#
# After:
#
Performance counter stats for './git fsck' (5 runs):
31605.868825 task-clock # 0.998 CPUs utilized ( +- 0.08% )
42 context-switches # 0.000 M/sec ( +- 3.92% )
0 CPU-migrations # 0.000 M/sec ( +-100.00% )
62,979 page-faults # 0.002 M/sec ( +- 14.72% )
101,297,181,916 cycles # 3.205 GHz ( +- 0.08% )
27,173,614,721 stalled-cycles # 26.83% of all cycles are idle ( +- 0.49% )
155,074,859,385 instructions # 1.53 insns per cycle
# 0.18 stalled cycles per insn ( +- 0.01% )
14,132,018,558 branches # 447.133 M/sec ( +- 0.02% )
1,207,054,592 branch-misses # 8.54% of all branches ( +- 0.03% ) 31.675135938 seconds time elapsed ( +- 0.08% )
so there's a +1.3% speedup.
But git fsck stalls are dominated by libz and other external libraries:
# Events: 30K stalled-cycles
#
# Overhead Command Shared Object Symbol
# ........ ....... ..................... ............................
#
36.13% git libz.so.1.2.5 [.] 0x90be
18.27% git libc-2.13.90.so [.] __memcpy_ssse3_back
13.68% git libcrypto.so.1.0.0d [.] sha1_block_data_order
5.85% git libz.so.1.2.5 [.] inflate
4.69% git git [.] lookup_object
4.58% git libz.so.1.2.5 [.] adler32
4.30% git libz.so.1.2.5 [.] 0xc280
2.19% git libc-2.13.90.so [.] _int_mallocSo those dominate execution time.
Ingo