• Sergey Senozhatsky's avatar
    zram: switch to crypto compress API · ebaf9ab5
    Sergey Senozhatsky authored
    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.comSigned-off-by: default avatarSergey Senozhatsky <sergey.senozhatsky@gmail.com>
    Suggested-by: default avatarMinchan Kim <minchan@kernel.org>
    Suggested-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
    Acked-by: default avatarMinchan Kim <minchan@kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    ebaf9ab5
zcomp.c 5.93 KB