| Demonstrations of btrfsdist, the Linux eBPF/bcc version. |
| |
| |
| btrfsdist traces btrfs reads, writes, opens, and fsyncs, and summarizes their |
| latency as a power-of-2 histogram. For example: |
| |
| # ./btrfsdist |
| Tracing btrfs operation latency... Hit Ctrl-C to end. |
| ^C |
| |
| operation = 'read' |
| usecs : count distribution |
| 0 -> 1 : 15 | | |
| 2 -> 3 : 1308 |******* | |
| 4 -> 7 : 198 |* | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 11 | | |
| 32 -> 63 : 361 |* | |
| 64 -> 127 : 55 | | |
| 128 -> 255 : 104 | | |
| 256 -> 511 : 7312 |****************************************| |
| 512 -> 1023 : 387 |** | |
| 1024 -> 2047 : 10 | | |
| 2048 -> 4095 : 4 | | |
| |
| operation = 'write' |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 4 |****************************************| |
| |
| operation = 'open' |
| usecs : count distribution |
| 0 -> 1 : 1 |********** | |
| 2 -> 3 : 4 |****************************************| |
| |
| This output shows a bi-modal distribution for read latency, with a faster |
| mode of 1,308 reads that took between 2 and 3 microseconds, and a slower |
| mode of over 7,312 reads that took between 256 and 511 microseconds. 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, two second summaries, five times: |
| |
| # ./btrfsdist 2 5 |
| Tracing btrfs operation latency... Hit Ctrl-C to end. |
| |
| 03:40:49: |
| |
| operation = 'read' |
| usecs : count distribution |
| 0 -> 1 : 15 | | |
| 2 -> 3 : 833 |******** | |
| 4 -> 7 : 127 |* | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 8 | | |
| 32 -> 63 : 907 |******** | |
| 64 -> 127 : 91 | | |
| 128 -> 255 : 246 |** | |
| 256 -> 511 : 4164 |****************************************| |
| 512 -> 1023 : 193 |* | |
| 1024 -> 2047 : 4 | | |
| 2048 -> 4095 : 6 | | |
| 4096 -> 8191 : 2 | | |
| |
| 03:40:51: |
| |
| operation = 'read' |
| usecs : count distribution |
| 0 -> 1 : 25 | | |
| 2 -> 3 : 1491 |*************** | |
| 4 -> 7 : 218 |** | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 16 | | |
| 32 -> 63 : 1527 |*************** | |
| 64 -> 127 : 319 |*** | |
| 128 -> 255 : 429 |**** | |
| 256 -> 511 : 3841 |****************************************| |
| 512 -> 1023 : 232 |** | |
| 1024 -> 2047 : 3 | | |
| 2048 -> 4095 : 6 | | |
| 4096 -> 8191 : 1 | | |
| 8192 -> 16383 : 1 | | |
| |
| 03:40:53: |
| |
| operation = 'read' |
| usecs : count distribution |
| 0 -> 1 : 27 | | |
| 2 -> 3 : 2999 |********************************* | |
| 4 -> 7 : 407 |**** | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 46 | | |
| 32 -> 63 : 3538 |****************************************| |
| 64 -> 127 : 595 |****** | |
| 128 -> 255 : 621 |******* | |
| 256 -> 511 : 3532 |*************************************** | |
| 512 -> 1023 : 212 |** | |
| 1024 -> 2047 : 1 | | |
| 2048 -> 4095 : 0 | | |
| 4096 -> 8191 : 0 | | |
| 8192 -> 16383 : 0 | | |
| 16384 -> 32767 : 1 | | |
| |
| 03:40:55: |
| |
| operation = 'read' |
| usecs : count distribution |
| 0 -> 1 : 221 | | |
| 2 -> 3 : 12580 |****************************************| |
| 4 -> 7 : 1366 |**** | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 289 | | |
| 32 -> 63 : 10782 |********************************** | |
| 64 -> 127 : 1232 |*** | |
| 128 -> 255 : 807 |** | |
| 256 -> 511 : 2299 |******* | |
| 512 -> 1023 : 135 | | |
| 1024 -> 2047 : 5 | | |
| 2048 -> 4095 : 2 | | |
| |
| 03:40:57: |
| |
| operation = 'read' |
| usecs : count distribution |
| 0 -> 1 : 73951 |************************* | |
| 2 -> 3 : 117639 |****************************************| |
| 4 -> 7 : 7943 |** | |
| 8 -> 15 : 1841 | | |
| 16 -> 31 : 1143 | | |
| 32 -> 63 : 5006 |* | |
| 64 -> 127 : 483 | | |
| 128 -> 255 : 242 | | |
| 256 -> 511 : 253 | | |
| 512 -> 1023 : 84 | | |
| 1024 -> 2047 : 23 | | |
| |
| This shows a read workload that begins bimodal, and eventually the second |
| mode disappears. The reason for this is that the workload cached during |
| tracing. Note that the rate also increased, with over 200k reads for the |
| final two second sample. |
| |
| |
| USAGE message: |
| |
| # ./btrfsdist -h |
| usage: btrfsdist [-h] [-T] [-m] [-p PID] [interval] [count] |
| |
| Summarize btrfs 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: |
| ./btrfsdist # show operation latency as a histogram |
| ./btrfsdist -p 181 # trace PID 181 only |
| ./btrfsdist 1 10 # print 1 second summaries, 10 times |
| ./btrfsdist -m 5 # 5s summaries, milliseconds |
