On Sat, Mar 13, 2021 at 09:49:23AM +0100, Borislav Petkov wrote:
> Lemme rerun here with clang.
clang11 is almost twice as slow as gcc but difference is still
negligible: ~0.6 seconds.
./tools/perf/perf stat --repeat 5 --sync --pre=/root/bin/pre-build-kernel.sh --
make -s -j9 LLVM=1 LLVM_IAS=1 bzImage
before:
Performance counter stats for 'make -s -j9 LLVM=1 LLVM_IAS=1 bzImage' (5 runs):
5,576,081.48 msec task-clock # 7.664 CPUs utilized
( +- 0.03% )
496,841 context-switches # 0.089 K/sec
( +- 0.11% )
30,245 cpu-migrations # 0.005 K/sec
( +- 0.53% )
49,702,714 page-faults # 0.009 M/sec
( +- 0.00% )
19,954,704,926,347 cycles # 3.579 GHz
( +- 0.02% ) (83.33%)
15,920,125,996,460 stalled-cycles-frontend # 79.78% frontend cycles
idle ( +- 0.03% ) (83.33%)
13,177,812,137,935 stalled-cycles-backend # 66.04% backend cycles
idle ( +- 0.04% ) (66.67%)
8,778,060,061,848 instructions # 0.44 insn per cycle
# 1.81 stalled cycles per
insn ( +- 0.00% ) (83.33%)
1,852,121,066,032 branches # 332.155 M/sec
( +- 0.00% ) (83.33%)
84,048,262,434 branch-misses # 4.54% of all branches
( +- 0.02% ) (83.33%)
727.572 +- 0.305 seconds time elapsed ( +- 0.04% )
after:
Performance counter stats for 'make -s -j9 LLVM=1 LLVM_IAS=1 bzImage' (5 runs):
5,581,654.38 msec task-clock # 7.665 CPUs utilized
( +- 0.01% )
496,274 context-switches # 0.089 K/sec
( +- 0.12% )
30,645 cpu-migrations # 0.005 K/sec
( +- 0.54% )
49,711,551 page-faults # 0.009 M/sec
( +- 0.01% )
19,968,933,753,686 cycles # 3.578 GHz
( +- 0.01% ) (83.33%)
15,925,776,797,854 stalled-cycles-frontend # 79.75% frontend cycles
idle ( +- 0.01% ) (83.33%)
13,182,158,323,446 stalled-cycles-backend # 66.01% backend cycles
idle ( +- 0.01% ) (66.67%)
8,778,619,885,119 instructions # 0.44 insn per cycle
# 1.81 stalled cycles per
insn ( +- 0.00% ) (83.33%)
1,852,096,100,464 branches # 331.818 M/sec
( +- 0.01% ) (83.33%)
84,264,257,355 branch-misses # 4.55% of all branches
( +- 0.03% ) (83.33%)
728.2400 +- 0.0613 seconds time elapsed ( +- 0.01% )
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
