perf stat结果，周期为25806004593，32个线程的经过时间为0.527408365秒。但2个线程周期为4109847315，经过的时间为1.075951973秒。
为什么周期如此之多？周期不是时钟周期??????
32个帖子：
13514.208793 task-clock # 25.624 CPUs utilized ( +- 0.48% )
2,440 context-switches # 0.000 M/sec ( +- 0.85% )
38 CPU-migrations # 0.000 M/sec ( +- 2.63% )
343,594 page-faults # 0.025 M/sec ( +- 0.00% )
25,806,004,593 cycles # 1.910 GHz ( +- 0.00% ) [40.31%]
22,793,327,794 stalled-cycles-frontend # 88.33% frontend cycles idle ( +- 0.38% ) [40.16%]
4,841,643,161 stalled-cycles-backend # 18.76% backend cycles idle ( +- 2.60% ) [40.38%]
5,661,365,666 instructions # 0.22 insns per cycle
# 4.03 stalled cycles per insn ( +- 0.29% ) [50.40%]
572,831,916 branches # 42.387 M/sec ( +- 0.22% ) [50.30%]
377,057 branch-misses # 0.07% of all branches ( +- 9.16% ) [50.52%]
2,954,860,090 L1-dcache-loads # 218.648 M/sec ( +- 0.44% ) [50.53%]
29,016,874 L1-dcache-load-misses # 0.98% of all L1-dcache hits ( +- 1.90% ) [50.63%]
5,855,196 LLC-loads # 0.433 M/sec ( +- 12.92% ) [40.55%]
3,771,211 LLC-load-misses # 64.41% of all LL-cache hits ( +- 14.39% ) [40.55%]
0.527408365 seconds time elapsed ( +- 0.80% )
2个主题：
2084.894924 task-clock # 1.938 CPUs utilized ( +- 0.03% )
183 context-switches # 0.000 M/sec ( +- 1.42% )
2 CPU-migrations # 0.000 M/sec ( +- 14.29% )
343,508 page-faults # 0.165 M/sec ( +- 0.00% )
4,109,847,315 cycles # 1.971 GHz ( +- 0.10% ) [39.77%]
1,039,138,688 stalled-cycles-frontend # 25.28% frontend cycles idle ( +- 0.95% ) [40.29%]
399,472,486 stalled-cycles-backend # 9.72% backend cycles idle ( +- 3.78% ) [40.71%]
5,555,427,341 instructions # 1.35 insns per cycle
# 0.19 stalled cycles per insn ( +- 0.17% ) [50.80%]
553,688,310 branches # 265.571 M/sec ( +- 0.19% ) [50.96%]
45,997 branch-misses # 0.01% of all branches ( +- 11.66% ) [50.94%]
2,940,653,305 L1-dcache-loads # 1410.456 M/sec ( +- 0.16% ) [50.54%]
25,312,789 L1-dcache-load-misses # 0.86% of all L1-dcache hits ( +- 0.09% ) [50.02%]
2,266,586 LLC-loads # 1.087 M/sec ( +- 1.49% ) [39.57%]
1,290,962 LLC-load-misses # 56.96% of all LL-cache hits ( +- 3.84% ) [39.49%]
1.075951973 seconds time elapsed ( +- 0.14% )