[問題] 使用mlockall不能完全避免page fault?

看板LinuxDev作者wtchen (沒有存在感的人)時間10年前 (2015/10/29 01:49)推噓3(3推 0噓 15→)

留言18則, 3人參與討論串1/1

正在試著評估RPi中如果用mlockall把memory鎖住會不會改善latency 用著名的cyclictest (v0.92)+perf得到以下結果： sudo perf stat ./cyclictest -p 90 - m -c 0 -i 3000 -n -h 250 -q -l 10000 # Total: 000009985 # Min Latencies: 00038 # Avg Latencies: 00082 # Max Latencies: 00386 # Histogram Overflows: 00015 Performance counter stats for './cyclictest -p 90 -m -c 0 -i 3000 -n -h 250 -q -l 10000': 818.925000 task-clock (msec) # 0.027 CPUs utilized 13,362 context-switches # 0.016 M/sec 0 cpu-migrations # 0.000 K/sec 56 page-faults # 0.068 K/sec 471,078,551 cycles # 0.575 GHz (50.34%) 282,495,112 stalled-cycles-frontend # 59.97% frontend cycles idle (51.67%) 13,419,172 stalled-cycles-backend # 2.85% backend cycles idle (52.93%) 68,489,877 instructions # 0.15 insns per cycle # 4.12 stalled cycles per insn (38.41%) 7,553,254 branches # 9.223 M/sec (30.02%) 1,627,813 branch-misses # 21.55% of all branches (34.01%) 30.232651000 seconds time elapsed 如果不加-m參數(不用mlockall)： sudo perf stat ./cyclictest -p 90 -c 0 -i 3000 -n -h 250 -q -l 10000 # Total: 000009988 # Min Latencies: 00038 # Avg Latencies: 00080 # Max Latencies: 00407 # Histogram Overflows: 00012 Performance counter stats for './cyclictest -p 90 -c 0 -i 3000 -n -h 250 -q -l 10000': 772.978000 task-clock (msec) # 0.026 CPUs utilized 13,363 context-switches # 0.017 M/sec 0 cpu-migrations # 0.000 K/sec 66 page-faults # 0.085 K/sec 444,135,743 cycles # 0.575 GHz (41.26%) 271,762,254 stalled-cycles-frontend # 61.19% frontend cycles idle (48.87%) 8,522,179 stalled-cycles-backend # 1.92% backend cycles idle (56.53%) 65,640,536 instructions # 0.15 insns per cycle # 4.14 stalled cycles per insn (37.62%) 7,453,674 branches # 9.643 M/sec (34.44%) 1,584,489 branch-misses # 21.26% of all branches (25.24%) 30.197211000 seconds time elapsed 看起來Max latencies會因為-m變小一點我的問題在於，page-faults只有因為-m變稍小一點，並沒有完全解決請問這是正常的嗎？我還以為mlockall住就不會有PF了。感謝 -- ※ 發信站: 批踢踢實業坊(ptt.cc), 來自: 90.41.67.118 ※ 文章網址: https://www.ptt.cc/bbs/LinuxDev/M.1446054583.A.EB6.html

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yvb

10/29 16:24, , 1^F

10/29 16:24, 1^F

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wtchen

10/29 19:28, , 2^F

10/29 19:28, 2^F

做了個實驗：把loop提高10倍看PF次數有沒有提高有mlockall的情況下：page-faults維持在55-56沒增加 Performance counter stats for './cyclictest -p 90 -m -c 0 -i 3000 -n -h 250 -q -l 100000': 7202.248000 task-clock (msec) # 0.024 CPUs utilized 130,818 context-switches # 0.018 M/sec 0 cpu-migrations # 0.000 K/sec 55 page-faults # 0.008 K/sec 4,079,431,733 cycles # 0.566 GHz (48.12%) 2,569,771,515 stalled-cycles-frontend # 62.99% frontend cycles idle (49.99%) 69,883,756 stalled-cycles-backend # 1.71% backend cycles idle (51.78%) 643,633,565 instructions # 0.16 insns per cycle # 3.99 stalled cycles per insn (34.40%) 72,253,517 branches # 10.032 M/sec (32.91%) 15,166,468 branch-misses # 20.99% of all branches (31.47%) 300.240982143 seconds time elapsed 沒有mlockall：page-faults維持在66-67 Performance counter stats for './cyclictest -p 90 -c 0 -i 3000 -n -h 250 -q -l 100000': 7181.634000 task-clock (msec) # 0.024 CPUs utilized 130,892 context-switches # 0.018 M/sec 0 cpu-migrations # 0.000 K/sec 67 page-faults # 0.009 K/sec 4,072,629,665 cycles # 0.567 GHz (49.76%) 2,537,027,318 stalled-cycles-frontend # 62.29% frontend cycles idle (49.79%) 70,191,503 stalled-cycles-backend # 1.72% backend cycles idle (50.05%) 627,997,620 instructions # 0.15 insns per cycle # 4.04 stalled cycles per insn (34.31%) 71,914,012 branches # 10.014 M/sec (33.07%) 15,190,645 branch-misses # 21.12% of all branches (33.44%) 300.195795144 seconds time elapsed 看起來loop增加並沒有增加page-faults... (不管有無mlockall) ※ 編輯: wtchen (90.41.214.241), 10/29/2015 19:46:17 ※ 編輯: wtchen (90.41.214.241), 10/29/2015 19:51:13