| Brendan Gregg | 1dcedc4 | 2016-02-12 02:29:08 -0800 | [diff] [blame] | 1 | Demonstrations of ext4dist, the Linux eBPF/bcc version. |
| 2 | |
| 3 | |
| 4 | ext4dist traces ext4 reads, writes, opens, and fsyncs, and summarizes their |
| 5 | latency as a power-of-2 histogram. For example: |
| 6 | |
| 7 | # ./ext4dist |
| 8 | Tracing ext4 operation latency... Hit Ctrl-C to end. |
| 9 | ^C |
| 10 | |
| 11 | operation = 'read' |
| 12 | usecs : count distribution |
| 13 | 0 -> 1 : 1210 |****************************************| |
| 14 | 2 -> 3 : 126 |**** | |
| 15 | 4 -> 7 : 376 |************ | |
| 16 | 8 -> 15 : 86 |** | |
| 17 | 16 -> 31 : 9 | | |
| 18 | 32 -> 63 : 47 |* | |
| 19 | 64 -> 127 : 6 | | |
| 20 | 128 -> 255 : 24 | | |
| 21 | 256 -> 511 : 137 |**** | |
| 22 | 512 -> 1023 : 66 |** | |
| 23 | 1024 -> 2047 : 13 | | |
| 24 | 2048 -> 4095 : 7 | | |
| 25 | 4096 -> 8191 : 13 | | |
| 26 | 8192 -> 16383 : 3 | | |
| 27 | |
| 28 | operation = 'write' |
| 29 | usecs : count distribution |
| 30 | 0 -> 1 : 0 | | |
| 31 | 2 -> 3 : 0 | | |
| 32 | 4 -> 7 : 0 | | |
| 33 | 8 -> 15 : 75 |****************************************| |
| 34 | 16 -> 31 : 5 |** | |
| 35 | |
| 36 | operation = 'open' |
| 37 | usecs : count distribution |
| 38 | 0 -> 1 : 1278 |****************************************| |
| 39 | 2 -> 3 : 40 |* | |
| 40 | 4 -> 7 : 4 | | |
| 41 | 8 -> 15 : 1 | | |
| 42 | 16 -> 31 : 1 | | |
| 43 | |
| 44 | This output shows a bi-modal distribution for read latency, with a faster |
| 45 | mode of less than 7 microseconds, and a slower mode of between 256 and 1023 |
| 46 | microseconds. The count column shows how many events fell into that latency |
| 47 | range. It's likely that the faster mode was a hit from the in-memory file |
| 48 | system cache, and the slower mode is a read from a storage device (disk). |
| 49 | |
| 50 | This "latency" is measured from when the operation was issued from the VFS |
| 51 | interface to the file system, to when it completed. This spans everything: |
| 52 | block device I/O (disk I/O), file system CPU cycles, file system locks, run |
| 53 | queue latency, etc. This is a better measure of the latency suffered by |
| 54 | applications reading from the file system than measuring this down at the |
| 55 | block device interface. |
| 56 | |
| 57 | Note that this only traces the common file system operations previously |
| 58 | listed: other file system operations (eg, inode operations including |
| 59 | getattr()) are not traced. |
| 60 | |
| 61 | |
| 62 | An optional interval and a count can be provided, as well as -m to show the |
| 63 | distributions in milliseconds. For example: |
| 64 | |
| 65 | # ./ext4dist -m 1 5 |
| 66 | Tracing ext4 operation latency... Hit Ctrl-C to end. |
| 67 | |
| 68 | 10:19:00: |
| 69 | |
| 70 | operation = 'read' |
| 71 | msecs : count distribution |
| 72 | 0 -> 1 : 576 |****************************************| |
| 73 | 2 -> 3 : 5 | | |
| 74 | 4 -> 7 : 6 | | |
| 75 | 8 -> 15 : 13 | | |
| 76 | 16 -> 31 : 17 |* | |
| 77 | 32 -> 63 : 5 | | |
| 78 | 64 -> 127 : 1 | | |
| 79 | |
| 80 | operation = 'write' |
| 81 | msecs : count distribution |
| 82 | 0 -> 1 : 20 |****************************************| |
| 83 | |
| 84 | operation = 'open' |
| 85 | msecs : count distribution |
| 86 | 0 -> 1 : 346 |****************************************| |
| 87 | |
| 88 | 10:19:01: |
| 89 | |
| 90 | operation = 'read' |
| 91 | msecs : count distribution |
| 92 | 0 -> 1 : 584 |****************************************| |
| 93 | 2 -> 3 : 10 | | |
| 94 | 4 -> 7 : 11 | | |
| 95 | 8 -> 15 : 16 |* | |
| 96 | 16 -> 31 : 6 | | |
| 97 | 32 -> 63 : 4 | | |
| 98 | 64 -> 127 : 2 | | |
| 99 | 128 -> 255 : 1 | | |
| 100 | |
| 101 | operation = 'write' |
| 102 | msecs : count distribution |
| 103 | 0 -> 1 : 20 |****************************************| |
| 104 | |
| 105 | operation = 'open' |
| 106 | msecs : count distribution |
| 107 | 0 -> 1 : 336 |****************************************| |
| 108 | |
| 109 | 10:19:02: |
| 110 | |
| 111 | operation = 'read' |
| 112 | msecs : count distribution |
| 113 | 0 -> 1 : 678 |****************************************| |
| 114 | 2 -> 3 : 7 | | |
| 115 | 4 -> 7 : 9 | | |
| 116 | 8 -> 15 : 25 |* | |
| 117 | 16 -> 31 : 10 | | |
| 118 | 32 -> 63 : 3 | | |
| 119 | |
| 120 | operation = 'write' |
| 121 | msecs : count distribution |
| 122 | 0 -> 1 : 19 |****************************************| |
| 123 | 2 -> 3 : 1 |** | |
| 124 | |
| 125 | operation = 'open' |
| 126 | msecs : count distribution |
| 127 | 0 -> 1 : 390 |****************************************| |
| 128 | |
| 129 | 10:19:03: |
| 130 | |
| 131 | operation = 'read' |
| 132 | msecs : count distribution |
| 133 | 0 -> 1 : 567 |****************************************| |
| 134 | 2 -> 3 : 7 | | |
| 135 | 4 -> 7 : 9 | | |
| 136 | 8 -> 15 : 20 |* | |
| 137 | 16 -> 31 : 15 |* | |
| 138 | 32 -> 63 : 5 | | |
| 139 | 64 -> 127 : 2 | | |
| 140 | |
| 141 | operation = 'write' |
| 142 | msecs : count distribution |
| 143 | 0 -> 1 : 20 |****************************************| |
| 144 | |
| 145 | operation = 'open' |
| 146 | msecs : count distribution |
| 147 | 0 -> 1 : 417 |****************************************| |
| 148 | |
| 149 | 10:19:04: |
| 150 | |
| 151 | operation = 'read' |
| 152 | msecs : count distribution |
| 153 | 0 -> 1 : 762 |****************************************| |
| 154 | 2 -> 3 : 9 | | |
| 155 | 4 -> 7 : 9 | | |
| 156 | 8 -> 15 : 11 | | |
| 157 | 16 -> 31 : 20 |* | |
| 158 | 32 -> 63 : 4 | | |
| 159 | 64 -> 127 : 1 | | |
| 160 | |
| 161 | operation = 'write' |
| 162 | msecs : count distribution |
| 163 | 0 -> 1 : 20 |****************************************| |
| 164 | |
| 165 | operation = 'open' |
| 166 | msecs : count distribution |
| 167 | 0 -> 1 : 427 |****************************************| |
| 168 | |
| 169 | This shows a mixed read/write workload. |
| 170 | |
| 171 | |
| 172 | USAGE message: |
| 173 | |
| 174 | # ./ext4dist -h |
| 175 | usage: ext4dist [-h] [-T] [-m] [-p PID] [interval] [count] |
| 176 | |
| 177 | Summarize ext4 operation latency |
| 178 | |
| 179 | positional arguments: |
| 180 | interval output interval, in seconds |
| 181 | count number of outputs |
| 182 | |
| 183 | optional arguments: |
| 184 | -h, --help show this help message and exit |
| 185 | -T, --notimestamp don't include timestamp on interval output |
| 186 | -m, --milliseconds output in milliseconds |
| 187 | -p PID, --pid PID trace this PID only |
| 188 | |
| 189 | examples: |
| 190 | ./ext4dist # show operation latency as a histogram |
| 191 | ./ext4dist -p 181 # trace PID 181 only |
| 192 | ./ext4dist 1 10 # print 1 second summaries, 10 times |
| 193 | ./ext4dist -m 5 # 5s summaries, milliseconds |