1Demonstrations of zfsslower, the Linux eBPF/bcc version. 2 3 4zfsslower shows ZFS reads, writes, opens, and fsyncs, slower than a threshold. 5It has been written to work on ZFS on Linux (http://zfsonlinux.org). For 6example: 7 8# ./zfsslower 9Tracing ZFS operations slower than 10 ms 10TIME COMM PID T BYTES OFF_KB LAT(ms) FILENAME 1106:31:28 dd 25570 W 131072 38784 303.92 data1 1206:31:34 dd 25686 W 131072 38784 388.28 data1 1306:31:35 dd 25686 W 131072 78720 519.66 data1 1406:31:35 dd 25686 W 131072 116992 405.94 data1 1506:31:35 dd 25686 W 131072 153600 433.52 data1 1606:31:36 dd 25686 W 131072 188672 314.37 data1 1706:31:36 dd 25686 W 131072 222336 372.33 data1 1806:31:36 dd 25686 W 131072 254592 309.59 data1 1906:31:37 dd 25686 W 131072 285440 304.52 data1 2006:31:37 dd 25686 W 131072 315008 236.45 data1 2106:31:37 dd 25686 W 131072 343424 193.54 data1 2206:31:38 dd 25686 W 131072 370560 286.07 data1 2306:31:38 dd 25686 W 131072 396672 251.92 data1 24[...] 25 26This shows writes to a "data1" file, each taking well over the 10 ms threshold. 27the slowest, on the 3rd line of output, reached 519.66 ms for a 128 Kbyte 28write by the "dd" command. 29 30This "latency" is measured from when the operation was issued from the VFS 31interface to the file system (via the ZFS POSIX layer), to when it completed. 32This spans everything: block device I/O (disk I/O), file system CPU cycles, 33file system locks, run queue latency, etc. This is a better measure of the 34latency suffered by applications reading from the file system than measuring 35this down at the block device interface. 36 37Note that this only traces the common file system operations previously 38listed: other file system operations (eg, inode operations including 39getattr()) are not traced. 40 41 42A threshold of 0 will trace all operations. Warning: the output will be 43verbose, as it will include all file system cache hits. 44 45# ./zfsslower 0 46Tracing ZFS operations 47TIME COMM PID T BYTES OFF_KB LAT(ms) FILENAME 4806:36:07 dd 32242 O 0 0 0.01 data1 4906:36:07 dd 32242 W 131072 0 0.25 data1 5006:36:07 dd 32242 W 131072 128 0.03 data1 5106:36:07 dd 32242 W 131072 256 0.04 data1 5206:36:07 dd 32242 W 131072 384 0.04 data1 5306:36:07 dd 32242 W 131072 512 0.04 data1 5406:36:07 dd 32242 W 131072 640 0.03 data1 5506:36:07 dd 32242 W 131072 768 0.03 data1 5606:36:07 dd 32242 W 131072 896 0.04 data1 5706:36:07 dd 32242 W 131072 1024 0.28 data1 5806:36:07 dd 32242 W 131072 1152 0.04 data1 5906:36:07 dd 32242 W 131072 1280 0.03 data1 60[...] 6106:36:07 dd 32242 W 131072 13824 0.04 data1 6206:36:07 dd 32242 W 131072 13952 0.04 data1 6306:36:07 dd 32242 W 131072 14080 0.04 data1 6406:36:07 dd 32242 W 131072 14208 398.92 data1 6506:36:07 dd 32242 W 131072 14336 0.04 data1 6606:36:07 dd 32242 W 131072 14464 0.04 data1 6706:36:07 dd 32242 W 131072 15104 0.03 data1 68[...] 69 70The output now includes the open operation for this file ("O"), and then the 71writes. Most of the writes are very fast, with only an occasional outlier that 72is in the hundreds of milliseconds. 73 74Fortunately this is not a real world environment: I setup a zpool on top of a 75XFS file system for testing purposes. More debugging using other tools will 76explain these outliers: possibly XFS flushing. 77 78 79Here's a random read workload, and showing operations slower than 1 ms: 80 81# ./zfsslower 1 82Tracing ZFS operations slower than 1 ms 83TIME COMM PID T BYTES OFF_KB LAT(ms) FILENAME 8406:47:30 randread.pl 15431 R 8192 97840 1.03 data1 8506:47:30 randread.pl 15431 R 8192 416744 1.12 data1 8606:47:31 randread.pl 15431 R 8192 228856 1.96 data1 8706:47:31 randread.pl 15431 R 8192 452248 1.02 data1 8806:47:31 randread.pl 15431 R 8192 315288 5.90 data1 8906:47:31 randread.pl 15431 R 8192 752696 1.20 data1 9006:47:31 randread.pl 15431 R 8192 481832 1.39 data1 9106:47:31 randread.pl 15431 R 8192 673752 1.39 data1 9206:47:31 randread.pl 15431 R 8192 691736 1.01 data1 9306:47:31 randread.pl 15431 R 8192 694776 1.78 data1 9406:47:31 randread.pl 15431 R 8192 403328 3.75 data1 9506:47:31 randread.pl 15431 R 8192 567688 1.08 data1 9606:47:31 randread.pl 15431 R 8192 694280 1.31 data1 9706:47:31 randread.pl 15431 R 8192 669280 1.06 data1 9806:47:31 randread.pl 15431 R 8192 426608 1.56 data1 9906:47:31 randread.pl 15431 R 8192 42512 1.01 data1 10006:47:31 randread.pl 15431 R 8192 22944 1.33 data1 10106:47:31 randread.pl 15431 R 8192 427432 1.48 data1 10206:47:31 randread.pl 15431 R 8192 261320 1.28 data1 10306:47:31 randread.pl 15431 R 8192 132248 1.23 data1 10406:47:31 randread.pl 15431 R 8192 96936 1.04 data1 10506:47:31 randread.pl 15431 R 8192 482800 2.63 data1 106[...] 107 108 109A -j option will print just the fields (parsable output, csv): 110 111# ./zfsslower -j 1 112ENDTIME_us,TASK,PID,TYPE,BYTES,OFFSET_b,LATENCY_us,FILE 113252305490911,randread.pl,17922,R,8192,163446784,1156,data1 114252305493852,randread.pl,17922,R,8192,321437696,1129,data1 115252305498839,randread.pl,17922,R,8192,475152384,1154,data1 116252305505515,randread.pl,17922,R,8192,49094656,1082,data1 117252305506774,randread.pl,17922,R,8192,470401024,1245,data1 118252305509265,randread.pl,17922,R,8192,553246720,2412,data1 119252305512365,randread.pl,17922,R,8192,20963328,1093,data1 120252305513755,randread.pl,17922,R,8192,304111616,1350,data1 121252305583330,randread.pl,17922,R,8192,166174720,1154,data1 122252305593913,randread.pl,17922,R,8192,175079424,1241,data1 123252305602833,randread.pl,17922,R,8192,305340416,3307,data1 124252305608663,randread.pl,17922,R,8192,655958016,2704,data1 125252305611212,randread.pl,17922,R,8192,40951808,1033,data1 126252305614609,randread.pl,17922,R,8192,318922752,2687,data1 127252305623800,randread.pl,17922,R,8192,246734848,2983,data1 128252305711125,randread.pl,17922,R,8192,581795840,1091,data1 129252305728694,randread.pl,17922,R,8192,710483968,1034,data1 130252305762046,randread.pl,17922,R,8192,329367552,1405,data1 131252305798215,randread.pl,17922,R,8192,44482560,1030,data1 132252305806748,randread.pl,17922,R,8192,660602880,1069,data1 133252305826360,randread.pl,17922,R,8192,616144896,2327,data1 134[...] 135 136 137USAGE message: 138 139# ./zfsslower -h 140usage: zfsslower [-h] [-j] [-p PID] [min_ms] 141 142Trace common ZFS file operations slower than a threshold 143 144positional arguments: 145 min_ms minimum I/O duration to trace, in ms (default 10) 146 147optional arguments: 148 -h, --help show this help message and exit 149 -j, --csv just print fields: comma-separated values 150 -p PID, --pid PID trace this PID only 151 152examples: 153 ./zfsslower # trace operations slower than 10 ms (default) 154 ./zfsslower 1 # trace operations slower than 1 ms 155 ./zfsslower -j 1 # ... 1 ms, parsable output (csv) 156 ./zfsslower 0 # trace all operations (warning: verbose) 157 ./zfsslower -p 185 # trace PID 185 only 158