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ebaf9ab56d
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.
Also update zcomp interface to be more aligned with the crypto API.
[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
Link: http://lkml.kernel.org/r/20160531122017.2878-3-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Suggested-by: Minchan Kim <minchan@kernel.org>
Suggested-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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