Re: [PATCH v2 2/8] zram: switch to crypto compress API

From: Minchan Kim
Date: Tue May 31 2016 - 19:40:07 EST

On Tue, May 31, 2016 at 09:20:11PM +0900, Sergey Senozhatsky wrote:
> We don't have an idle zstreams list anymore and our write path
> now works absolutely differently, preventing preemption during
> compression. This removes possibilities of read paths preempting
> writes at wrong places (which could badly affect the performance
> of both paths) and at the same time opens the door for a move
> from custom LZO/LZ4 compression backends implementation to a more
> generic one, using crypto compress API.
>
> Joonsoo Kim [1] attempted to do this a while ago, but faced with
> the need of introducing a new crypto API interface. The root cause
> was the fact that crypto API compression algorithms require a
> compression stream structure (in zram terminology) for both
> compression and decompression ops, while in reality only several
> of compression algorithms really need it. This resulted in a
> concept of context-less crypto API compression backends [2]. Both
> write and read paths, though, would have been executed with the
> preemption enabled, which in the worst case could have resulted
> in a decreased worst-case performance, e.g. consider the
> following case:
>
> CPU0
>
> zram_write()
> spin_lock()
> take the last idle stream
> spin_unlock()
>
> << preempted >>
>
> zram_read()
> spin_lock()
> no idle streams
> spin_unlock()
> schedule()
>
> resuming zram_write compression()
>
> but it took me some time to realize that, and it took even longer
> to evolve zram and to make it ready for crypto API. The key turned
> out to be -- drop the idle streams list entirely. Without the idle
> streams list we are free to use compression algorithms that require
> compression stream for decompression (read), because streams are
> now placed in per-cpu data and each write path has to disable
> preemption for compression op, almost completely eliminating the
> aforementioned case (technically, we still have a small chance,
> because write path has a fast and a slow paths and the slow path
> is executed with the preemption enabled; but the frequency of
> failed fast path is too low).
>
> TEST
> ====
>
> - 4 CPUs, x86_64 system
> - 3G zram, lzo
> - fio tests: read, randread, write, randwrite, rw, randrw
>
> test script [3] command:
> ZRAM_SIZE=3G LOG_SUFFIX=XXXX FIO_LOOPS=5 ./zram-fio-test.sh
>
> BASE PATCHED
> jobs1
> READ: 2527.2MB/s 2482.7MB/s
> READ: 2102.7MB/s 2045.0MB/s
> WRITE: 1284.3MB/s 1324.3MB/s
> WRITE: 1080.7MB/s 1101.9MB/s
> READ: 430125KB/s 437498KB/s
> WRITE: 430538KB/s 437919KB/s
> READ: 399593KB/s 403987KB/s
> WRITE: 399910KB/s 404308KB/s
> jobs2
> READ: 8133.5MB/s 7854.8MB/s
> READ: 7086.6MB/s 6912.8MB/s
> WRITE: 3177.2MB/s 3298.3MB/s
> WRITE: 2810.2MB/s 2871.4MB/s
> READ: 1017.6MB/s 1023.4MB/s
> WRITE: 1018.2MB/s 1023.1MB/s
> READ: 977836KB/s 984205KB/s
> WRITE: 979435KB/s 985814KB/s
> jobs3
> READ: 13557MB/s 13391MB/s
> READ: 11876MB/s 11752MB/s
> WRITE: 4641.5MB/s 4682.1MB/s
> WRITE: 4164.9MB/s 4179.3MB/s
> READ: 1453.8MB/s 1455.1MB/s
> WRITE: 1455.1MB/s 1458.2MB/s
> READ: 1387.7MB/s 1395.7MB/s
> WRITE: 1386.1MB/s 1394.9MB/s
> jobs4
> READ: 20271MB/s 20078MB/s
> READ: 18033MB/s 17928MB/s
> WRITE: 6176.8MB/s 6180.5MB/s
> WRITE: 5686.3MB/s 5705.3MB/s
> READ: 2009.4MB/s 2006.7MB/s
> WRITE: 2007.5MB/s 2004.9MB/s
> READ: 1929.7MB/s 1935.6MB/s
> WRITE: 1926.8MB/s 1932.6MB/s
> jobs5
> READ: 18823MB/s 19024MB/s
> READ: 18968MB/s 19071MB/s
> WRITE: 6191.6MB/s 6372.1MB/s
> WRITE: 5818.7MB/s 5787.1MB/s
> READ: 2011.7MB/s 1981.3MB/s
> WRITE: 2011.4MB/s 1980.1MB/s
> READ: 1949.3MB/s 1935.7MB/s
> WRITE: 1940.4MB/s 1926.1MB/s
> jobs6
> READ: 21870MB/s 21715MB/s
> READ: 19957MB/s 19879MB/s
> WRITE: 6528.4MB/s 6537.6MB/s
> WRITE: 6098.9MB/s 6073.6MB/s
> READ: 2048.6MB/s 2049.9MB/s
> WRITE: 2041.7MB/s 2042.9MB/s
> READ: 2013.4MB/s 1990.4MB/s
> WRITE: 2009.4MB/s 1986.5MB/s
> jobs7
> READ: 21359MB/s 21124MB/s
> READ: 19746MB/s 19293MB/s
> WRITE: 6660.4MB/s 6518.8MB/s
> WRITE: 6211.6MB/s 6193.1MB/s
> READ: 2089.7MB/s 2080.6MB/s
> WRITE: 2085.8MB/s 2076.5MB/s
> READ: 2041.2MB/s 2052.5MB/s
> WRITE: 2037.5MB/s 2048.8MB/s
> jobs8
> READ: 20477MB/s 19974MB/s
> READ: 18922MB/s 18576MB/s
> WRITE: 6851.9MB/s 6788.3MB/s
> WRITE: 6407.7MB/s 6347.5MB/s
> READ: 2134.8MB/s 2136.1MB/s
> WRITE: 2132.8MB/s 2134.4MB/s
> READ: 2074.2MB/s 2069.6MB/s
> WRITE: 2087.3MB/s 2082.4MB/s
> jobs9
> READ: 19797MB/s 19994MB/s
> READ: 18806MB/s 18581MB/s
> WRITE: 6878.7MB/s 6822.7MB/s
> WRITE: 6456.8MB/s 6447.2MB/s
> READ: 2141.1MB/s 2154.7MB/s
> WRITE: 2144.4MB/s 2157.3MB/s
> READ: 2084.1MB/s 2085.1MB/s
> WRITE: 2091.5MB/s 2092.5MB/s
> jobs10
> READ: 19794MB/s 19784MB/s
> READ: 18794MB/s 18745MB/s
> WRITE: 6984.4MB/s 6676.3MB/s
> WRITE: 6532.3MB/s 6342.7MB/s
> READ: 2150.6MB/s 2155.4MB/s
> WRITE: 2156.8MB/s 2161.5MB/s
> READ: 2106.4MB/s 2095.6MB/s
> WRITE: 2109.7MB/s 2098.4MB/s
>
> BASE PATCHED
> jobs1 perfstat
> stalled-cycles-frontend 102,480,595,419 ( 41.53%) 114,508,864,804 ( 46.92%)
> stalled-cycles-backend 51,941,417,832 ( 21.05%) 46,836,112,388 ( 19.19%)
> instructions 283,612,054,215 ( 1.15) 283,918,134,959 ( 1.16)
> branches 56,372,560,385 ( 724.923) 56,449,814,753 ( 733.766)
> branch-misses 374,826,000 ( 0.66%) 326,935,859 ( 0.58%)
> jobs2 perfstat
> stalled-cycles-frontend 155,142,745,777 ( 40.99%) 164,170,979,198 ( 43.82%)
> stalled-cycles-backend 70,813,866,387 ( 18.71%) 66,456,858,165 ( 17.74%)
> instructions 463,436,648,173 ( 1.22) 464,221,890,191 ( 1.24)
> branches 91,088,733,902 ( 760.088) 91,278,144,546 ( 769.133)
> branch-misses 504,460,363 ( 0.55%) 394,033,842 ( 0.43%)
> jobs3 perfstat
> stalled-cycles-frontend 201,300,397,212 ( 39.84%) 223,969,902,257 ( 44.44%)
> stalled-cycles-backend 87,712,593,974 ( 17.36%) 81,618,888,712 ( 16.19%)
> instructions 642,869,545,023 ( 1.27) 644,677,354,132 ( 1.28)
> branches 125,724,560,594 ( 690.682) 126,133,159,521 ( 694.542)
> branch-misses 527,941,798 ( 0.42%) 444,782,220 ( 0.35%)
> jobs4 perfstat
> stalled-cycles-frontend 246,701,197,429 ( 38.12%) 280,076,030,886 ( 43.29%)
> stalled-cycles-backend 119,050,341,112 ( 18.40%) 110,955,641,671 ( 17.15%)
> instructions 822,716,962,127 ( 1.27) 825,536,969,320 ( 1.28)
> branches 160,590,028,545 ( 688.614) 161,152,996,915 ( 691.068)
> branch-misses 650,295,287 ( 0.40%) 550,229,113 ( 0.34%)
> jobs5 perfstat
> stalled-cycles-frontend 298,958,462,516 ( 38.30%) 344,852,200,358 ( 44.16%)
> stalled-cycles-backend 137,558,742,122 ( 17.62%) 129,465,067,102 ( 16.58%)
> instructions 1,005,714,688,752 ( 1.29) 1,007,657,999,432 ( 1.29)
> branches 195,988,773,962 ( 697.730) 196,446,873,984 ( 700.319)
> branch-misses 695,818,940 ( 0.36%) 624,823,263 ( 0.32%)
> jobs6 perfstat
> stalled-cycles-frontend 334,497,602,856 ( 36.71%) 387,590,419,779 ( 42.38%)
> stalled-cycles-backend 163,539,365,335 ( 17.95%) 152,640,193,639 ( 16.69%)
> instructions 1,184,738,177,851 ( 1.30) 1,187,396,281,677 ( 1.30)
> branches 230,592,915,640 ( 702.902) 231,253,802,882 ( 702.356)
> branch-misses 747,934,786 ( 0.32%) 643,902,424 ( 0.28%)
> jobs7 perfstat
> stalled-cycles-frontend 396,724,684,187 ( 37.71%) 460,705,858,952 ( 43.84%)
> stalled-cycles-backend 188,096,616,496 ( 17.88%) 175,785,787,036 ( 16.73%)
> instructions 1,364,041,136,608 ( 1.30) 1,366,689,075,112 ( 1.30)
> branches 265,253,096,936 ( 700.078) 265,890,524,883 ( 702.839)
> branch-misses 784,991,589 ( 0.30%) 729,196,689 ( 0.27%)
> jobs8 perfstat
> stalled-cycles-frontend 440,248,299,870 ( 36.92%) 509,554,793,816 ( 42.46%)
> stalled-cycles-backend 222,575,930,616 ( 18.67%) 213,401,248,432 ( 17.78%)
> instructions 1,542,262,045,114 ( 1.29) 1,545,233,932,257 ( 1.29)
> branches 299,775,178,439 ( 697.666) 300,528,458,505 ( 694.769)
> branch-misses 847,496,084 ( 0.28%) 748,794,308 ( 0.25%)
> jobs9 perfstat
> stalled-cycles-frontend 506,269,882,480 ( 37.86%) 592,798,032,820 ( 44.43%)
> stalled-cycles-backend 253,192,498,861 ( 18.93%) 233,727,666,185 ( 17.52%)
> instructions 1,721,985,080,913 ( 1.29) 1,724,666,236,005 ( 1.29)
> branches 334,517,360,255 ( 694.134) 335,199,758,164 ( 697.131)
> branch-misses 873,496,730 ( 0.26%) 815,379,236 ( 0.24%)
> jobs10 perfstat
> stalled-cycles-frontend 549,063,363,749 ( 37.18%) 651,302,376,662 ( 43.61%)
> stalled-cycles-backend 281,680,986,810 ( 19.07%) 277,005,235,582 ( 18.55%)
> instructions 1,901,859,271,180 ( 1.29) 1,906,311,064,230 ( 1.28)
> branches 369,398,536,153 ( 694.004) 370,527,696,358 ( 688.409)
> branch-misses 967,929,335 ( 0.26%) 890,125,056 ( 0.24%)
>
> BASE PATCHED
> seconds elapsed 79.421641008 78.735285546
> seconds elapsed 61.471246133 60.869085949
> seconds elapsed 62.317058173 62.224188495
> seconds elapsed 60.030739363 60.081102518
> seconds elapsed 74.070398362 74.317582865
> seconds elapsed 84.985953007 85.414364176
> seconds elapsed 97.724553255 98.173311344
> seconds elapsed 109.488066758 110.268399318
> seconds elapsed 122.768189405 122.967164498
> seconds elapsed 135.130035105 136.934770801
>
> On my other system (8 x86_64 CPUs, short version of test results):
>
> BASE PATCHED
> seconds elapsed 19.518065994 19.806320662
> seconds elapsed 15.172772749 15.594718291
> seconds elapsed 13.820925970 13.821708564
> seconds elapsed 13.293097816 14.585206405
> seconds elapsed 16.207284118 16.064431606
> seconds elapsed 17.958376158 17.771825767
> seconds elapsed 19.478009164 19.602961508
> seconds elapsed 21.347152811 21.352318709
> seconds elapsed 24.478121126 24.171088735
> seconds elapsed 26.865057442 26.767327618
>
> So performance-wise the numbers are quite similar.
>
> [1] http://marc.info/?l=linux-kernel&m=144480832108927&w=2
> [2] http://marc.info/?l=linux-kernel&m=145379613507518&w=2
> [3] https://github.com/sergey-senozhatsky/zram-perf-test
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> Suggested-by: Minchan Kim <minchan@xxxxxxxxxx>
> Suggested-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>