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SubjectRe: [patch] get_request starvation fix
From

tiobench measurements using 2048 MB worth of files on ext2 fs.
K6-2 475 mhz with 384 MB RAM and IDE disk.
Sorted by test, number of threads, then kernel.
Read, write, and seek rates in MB/sec.
Latency in milliseconds.
Percent of requests that took longer than 2 and 10 seconds.

2.4.18-pre9-am1 = make_request, read_latency2, and low-latency patches.
2.4.18-pre9-am2 = make_request, read_latency2, and sync_livelock patches.

On sequential reads, kernels with make_request and read_latency2
reduce max latency from around 500 seconds down 2-8 seconds.
Fairness to requests is vastly improved. Throughput looks better too.

Sequential Reads Num Avg Maximum Lat% Lat%
Kernel Thr Rate (CPU%) Latency Latency >2s >10s
---------------- --- ---------------------------------------------------
2.4.18-pre9 32 9.18 12.19% 34.739 545388.95 0.00304 0.00304
2.4.18-pre9-ac1 32 11.48 30.08% 25.736 289601.71 0.00839 0.00839
2.4.18-pre9-am1 32 9.25 11.97% 40.103 2251.30 0.00000 0.00000
2.4.18-pre9-am2 32 9.32 12.11% 39.917 2206.14 0.00000 0.00000

2.4.18-pre9 64 8.83 11.81% 59.045 484270.65 0.02689 0.02651
2.4.18-pre9-ac1 64 10.37 27.12% 49.460 293425.91 0.04273 0.04196
2.4.18-pre9-am1 64 9.53 13.42% 77.737 3840.97 0.00000 0.00000
2.4.18-pre9-am2 64 9.52 13.15% 77.873 3951.99 0.00000 0.00000

2.4.18-pre9 128 8.44 10.92% 109.317 572551.72 0.08507 0.07534
2.4.18-pre9-ac1 128 9.28 24.08% 104.159 333550.33 0.13599 0.13523
2.4.18-pre9-am1 128 9.55 15.38% 153.480 7939.48 0.66070 0.00000
2.4.18-pre9-am2 128 9.59 15.72% 153.244 7648.12 0.80833 0.00000

On random reads, the make_request and read_latency2 patches help a lot at
128 threads. Max latency and % of high latency requests is greatly reduced.

Random Reads Num Avg Maximum Lat% Lat%
Kernel Thr Rate (CPU%) Latency Latency >2s >10s
---------------- --- ---------------------------------------------------
2.4.18-pre9 32 0.57 1.580% 549.367 1523.39 0.00000 0.00000
2.4.18-pre9-ac1 32 0.53 2.226% 660.193 2966.26 0.00000 0.00000
2.4.18-pre9-am1 32 0.58 1.479% 623.361 1693.90 0.00000 0.00000
2.4.18-pre9-am2 32 0.58 1.501% 619.679 1727.47 0.00000 0.00000

2.4.18-pre9 64 0.61 2.031% 1016.205 2618.34 0.00000 0.00000
2.4.18-pre9-ac1 64 0.56 2.579% 1160.377 72621.35 0.35283 0.32763
2.4.18-pre9-am1 64 0.61 1.711% 1145.865 2865.21 0.00000 0.00000
2.4.18-pre9-am2 64 0.62 1.978% 1135.097 2792.76 0.00000 0.00000

2.4.18-pre9 128 0.61 1.699% 1569.812 53372.49 4.48589 4.41029
2.4.18-pre9-ac1 128 0.55 2.701% 1862.139 75417.90 5.54435 5.21673
2.4.18-pre9-am1 128 0.63 2.511% 2152.480 4710.51 0.00000 0.00000
2.4.18-pre9-am2 128 0.63 2.525% 2145.578 4709.85 0.00000 0.00000

On the write tests, 2.4.18-pre9-ac1 has the best latency numbers.

Sequential Write Num Avg Maximum Lat% Lat%
Kernel Thr Rate (CPU%) Latency Latency >2s >10s
---------------- --- ---------------------------------------------------
2.4.18-pre9 32 13.18 35.47% 26.155 33677.84 0.48867 0.00324
2.4.18-pre9-ac1 32 13.66 36.82% 24.738 9008.30 0.03567 0.00000
2.4.18-pre9-am1 32 15.27 53.94% 21.236 39604.59 0.37098 0.00400
2.4.18-pre9-am2 32 15.17 53.66% 21.492 41358.77 0.37155 0.00496

2.4.18-pre9 64 13.47 44.74% 46.296 46673.56 0.76332 0.03968
2.4.18-pre9-ac1 64 11.91 32.45% 55.355 12051.19 0.22926 0.00000
2.4.18-pre9-am1 64 14.57 52.16% 43.430 51274.83 0.75874 0.05665
2.4.18-pre9-am2 64 14.78 53.76% 42.685 54281.45 0.63266 0.07457

2.4.18-pre9 128 12.78 42.55% 91.421 60494.19 1.20201 0.26531
2.4.18-pre9-ac1 128 10.15 27.63% 122.921 15371.80 1.29719 0.00000
2.4.18-pre9-am1 128 13.72 47.73% 83.373 69739.68 1.16043 0.22126
2.4.18-pre9-am2 128 14.17 52.81% 80.642 67952.87 1.10722 0.23041


Random Writes Num Avg Maximum Lat% Lat%
Kernel Thr Rate (CPU%) Latency Latency >2s >10s
---------------- --- ---------------------------------------------------
2.4.18-pre9 32 0.60 1.323% 1.915 576.55 0.00000 0.00000
2.4.18-pre9-ac1 32 0.61 1.296% 0.311 481.93 0.00000 0.00000
2.4.18-pre9-am1 32 0.71 2.411% 1.696 624.95 0.00000 0.00000
2.4.18-pre9-am2 32 0.73 2.804% 1.567 711.59 0.00000 0.00000

2.4.18-pre9 64 0.65 1.547% 1.552 558.61 0.00000 0.00000
2.4.18-pre9-ac1 64 0.64 1.457% 0.214 88.78 0.00000 0.00000
2.4.18-pre9-am1 64 0.74 2.649% 1.014 522.44 0.00000 0.00000
2.4.18-pre9-am2 64 0.75 2.647% 1.035 557.22 0.00000 0.00000

2.4.18-pre9 128 0.70 1.823% 1.664 785.13 0.00000 0.00000
2.4.18-pre9-ac1 128 0.67 1.926% 0.339 398.63 0.00000 0.00000
2.4.18-pre9-am1 128 0.76 2.716% 1.527 845.77 0.00000 0.00000
2.4.18-pre9-am2 128 0.75 2.828% 1.371 886.19 0.00000 0.00000

More tests on more kernels at
http://home.earthlink.net/~rwhron/kernel/k6-2-475.html
--
Randy Hron

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