| Demonstrations of ext4dist, the Linux eBPF/bcc version. |
| |
| |
| ext4dist traces ext4 reads, writes, opens, and fsyncs, and summarizes their |
| latency as a power-of-2 histogram. For example: |
| |
| # ./ext4dist |
| Tracing ext4 operation latency... Hit Ctrl-C to end. |
| ^C |
| |
| operation = 'read' |
| usecs : count distribution |
| 0 -> 1 : 1210 |****************************************| |
| 2 -> 3 : 126 |**** | |
| 4 -> 7 : 376 |************ | |
| 8 -> 15 : 86 |** | |
| 16 -> 31 : 9 | | |
| 32 -> 63 : 47 |* | |
| 64 -> 127 : 6 | | |
| 128 -> 255 : 24 | | |
| 256 -> 511 : 137 |**** | |
| 512 -> 1023 : 66 |** | |
| 1024 -> 2047 : 13 | | |
| 2048 -> 4095 : 7 | | |
| 4096 -> 8191 : 13 | | |
| 8192 -> 16383 : 3 | | |
| |
| operation = 'write' |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 75 |****************************************| |
| 16 -> 31 : 5 |** | |
| |
| operation = 'open' |
| usecs : count distribution |
| 0 -> 1 : 1278 |****************************************| |
| 2 -> 3 : 40 |* | |
| 4 -> 7 : 4 | | |
| 8 -> 15 : 1 | | |
| 16 -> 31 : 1 | | |
| |
| This output shows a bi-modal distribution for read latency, with a faster |
| mode of less than 7 microseconds, and a slower mode of between 256 and 1023 |
| microseconds. The count column shows how many events fell into that latency |
| range. It's likely that the faster mode was a hit from the in-memory file |
| system cache, and the slower mode is a read from a storage device (disk). |
| |
| This "latency" is measured from when the operation was issued from the VFS |
| interface to the file system, to when it completed. This spans everything: |
| block device I/O (disk I/O), file system CPU cycles, file system locks, run |
| queue latency, etc. This is a better measure of the latency suffered by |
| applications reading from the file system than measuring this down at the |
| block device interface. |
| |
| Note that this only traces the common file system operations previously |
| listed: other file system operations (eg, inode operations including |
| getattr()) are not traced. |
| |
| |
| An optional interval and a count can be provided, as well as -m to show the |
| distributions in milliseconds. For example: |
| |
| # ./ext4dist -m 1 5 |
| Tracing ext4 operation latency... Hit Ctrl-C to end. |
| |
| 10:19:00: |
| |
| operation = 'read' |
| msecs : count distribution |
| 0 -> 1 : 576 |****************************************| |
| 2 -> 3 : 5 | | |
| 4 -> 7 : 6 | | |
| 8 -> 15 : 13 | | |
| 16 -> 31 : 17 |* | |
| 32 -> 63 : 5 | | |
| 64 -> 127 : 1 | | |
| |
| operation = 'write' |
| msecs : count distribution |
| 0 -> 1 : 20 |****************************************| |
| |
| operation = 'open' |
| msecs : count distribution |
| 0 -> 1 : 346 |****************************************| |
| |
| 10:19:01: |
| |
| operation = 'read' |
| msecs : count distribution |
| 0 -> 1 : 584 |****************************************| |
| 2 -> 3 : 10 | | |
| 4 -> 7 : 11 | | |
| 8 -> 15 : 16 |* | |
| 16 -> 31 : 6 | | |
| 32 -> 63 : 4 | | |
| 64 -> 127 : 2 | | |
| 128 -> 255 : 1 | | |
| |
| operation = 'write' |
| msecs : count distribution |
| 0 -> 1 : 20 |****************************************| |
| |
| operation = 'open' |
| msecs : count distribution |
| 0 -> 1 : 336 |****************************************| |
| |
| 10:19:02: |
| |
| operation = 'read' |
| msecs : count distribution |
| 0 -> 1 : 678 |****************************************| |
| 2 -> 3 : 7 | | |
| 4 -> 7 : 9 | | |
| 8 -> 15 : 25 |* | |
| 16 -> 31 : 10 | | |
| 32 -> 63 : 3 | | |
| |
| operation = 'write' |
| msecs : count distribution |
| 0 -> 1 : 19 |****************************************| |
| 2 -> 3 : 1 |** | |
| |
| operation = 'open' |
| msecs : count distribution |
| 0 -> 1 : 390 |****************************************| |
| |
| 10:19:03: |
| |
| operation = 'read' |
| msecs : count distribution |
| 0 -> 1 : 567 |****************************************| |
| 2 -> 3 : 7 | | |
| 4 -> 7 : 9 | | |
| 8 -> 15 : 20 |* | |
| 16 -> 31 : 15 |* | |
| 32 -> 63 : 5 | | |
| 64 -> 127 : 2 | | |
| |
| operation = 'write' |
| msecs : count distribution |
| 0 -> 1 : 20 |****************************************| |
| |
| operation = 'open' |
| msecs : count distribution |
| 0 -> 1 : 417 |****************************************| |
| |
| 10:19:04: |
| |
| operation = 'read' |
| msecs : count distribution |
| 0 -> 1 : 762 |****************************************| |
| 2 -> 3 : 9 | | |
| 4 -> 7 : 9 | | |
| 8 -> 15 : 11 | | |
| 16 -> 31 : 20 |* | |
| 32 -> 63 : 4 | | |
| 64 -> 127 : 1 | | |
| |
| operation = 'write' |
| msecs : count distribution |
| 0 -> 1 : 20 |****************************************| |
| |
| operation = 'open' |
| msecs : count distribution |
| 0 -> 1 : 427 |****************************************| |
| |
| This shows a mixed read/write workload. |
| |
| |
| USAGE message: |
| |
| # ./ext4dist -h |
| usage: ext4dist [-h] [-T] [-m] [-p PID] [interval] [count] |
| |
| Summarize ext4 operation latency |
| |
| positional arguments: |
| interval output interval, in seconds |
| count number of outputs |
| |
| optional arguments: |
| -h, --help show this help message and exit |
| -T, --notimestamp don't include timestamp on interval output |
| -m, --milliseconds output in milliseconds |
| -p PID, --pid PID trace this PID only |
| |
| examples: |
| ./ext4dist # show operation latency as a histogram |
| ./ext4dist -p 181 # trace PID 181 only |
| ./ext4dist 1 10 # print 1 second summaries, 10 times |
| ./ext4dist -m 5 # 5s summaries, milliseconds |
