| Demonstrations of biolatency, the Linux eBPF/bcc version. |
| |
| |
| biolatency traces block device I/O (disk I/O), and records the distribution |
| of I/O latency (time), printing this as a histogram when Ctrl-C is hit. |
| For example: |
| |
| # ./biolatency |
| Tracing block device I/O... Hit Ctrl-C to end. |
| ^C |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 1 | | |
| 128 -> 255 : 12 |******** | |
| 256 -> 511 : 15 |********** | |
| 512 -> 1023 : 43 |******************************* | |
| 1024 -> 2047 : 52 |**************************************| |
| 2048 -> 4095 : 47 |********************************** | |
| 4096 -> 8191 : 52 |**************************************| |
| 8192 -> 16383 : 36 |************************** | |
| 16384 -> 32767 : 15 |********** | |
| 32768 -> 65535 : 2 |* | |
| 65536 -> 131071 : 2 |* | |
| |
| The latency of the disk I/O is measured from the issue to the device to its |
| completion. A -Q option can be used to include time queued in the kernel. |
| |
| This example output shows a large mode of latency from about 128 microseconds |
| to about 32767 microseconds (33 milliseconds). The bulk of the I/O was |
| between 1 and 8 ms, which is the expected block device latency for |
| rotational storage devices. |
| |
| The highest latency seen while tracing was between 65 and 131 milliseconds: |
| the last row printed, for which there were 2 I/O. |
| |
| For efficiency, biolatency uses an in-kernel eBPF map to store timestamps |
| with requests, and another in-kernel map to store the histogram (the "count") |
| column, which is copied to user-space only when output is printed. These |
| methods lower the performance overhead when tracing is performed. |
| |
| |
| In the following example, the -m option is used to print a histogram using |
| milliseconds as the units (which eliminates the first several rows), -T to |
| print timestamps with the output, and to print 1 second summaries 5 times: |
| |
| # ./biolatency -mT 1 5 |
| Tracing block device I/O... Hit Ctrl-C to end. |
| |
| 06:20:16 |
| msecs : count distribution |
| 0 -> 1 : 36 |**************************************| |
| 2 -> 3 : 1 |* | |
| 4 -> 7 : 3 |*** | |
| 8 -> 15 : 17 |***************** | |
| 16 -> 31 : 33 |********************************** | |
| 32 -> 63 : 7 |******* | |
| 64 -> 127 : 6 |****** | |
| |
| 06:20:17 |
| msecs : count distribution |
| 0 -> 1 : 96 |************************************ | |
| 2 -> 3 : 25 |********* | |
| 4 -> 7 : 29 |*********** | |
| 8 -> 15 : 62 |*********************** | |
| 16 -> 31 : 100 |**************************************| |
| 32 -> 63 : 62 |*********************** | |
| 64 -> 127 : 18 |****** | |
| |
| 06:20:18 |
| msecs : count distribution |
| 0 -> 1 : 68 |************************* | |
| 2 -> 3 : 76 |**************************** | |
| 4 -> 7 : 20 |******* | |
| 8 -> 15 : 48 |***************** | |
| 16 -> 31 : 103 |**************************************| |
| 32 -> 63 : 49 |****************** | |
| 64 -> 127 : 17 |****** | |
| |
| 06:20:19 |
| msecs : count distribution |
| 0 -> 1 : 522 |*************************************+| |
| 2 -> 3 : 225 |**************** | |
| 4 -> 7 : 38 |** | |
| 8 -> 15 : 8 | | |
| 16 -> 31 : 1 | | |
| |
| 06:20:20 |
| msecs : count distribution |
| 0 -> 1 : 436 |**************************************| |
| 2 -> 3 : 106 |********* | |
| 4 -> 7 : 34 |** | |
| 8 -> 15 : 19 |* | |
| 16 -> 31 : 1 | | |
| |
| How the I/O latency distribution changes over time can be seen. |
| |
| |
| |
| The -Q option begins measuring I/O latency from when the request was first |
| queued in the kernel, and includes queuing latency: |
| |
| # ./biolatency -Q |
| Tracing block device I/O... Hit Ctrl-C to end. |
| ^C |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 3 |* | |
| 256 -> 511 : 37 |************** | |
| 512 -> 1023 : 30 |*********** | |
| 1024 -> 2047 : 18 |******* | |
| 2048 -> 4095 : 22 |******** | |
| 4096 -> 8191 : 14 |***** | |
| 8192 -> 16383 : 48 |******************* | |
| 16384 -> 32767 : 96 |**************************************| |
| 32768 -> 65535 : 31 |************ | |
| 65536 -> 131071 : 26 |********** | |
| 131072 -> 262143 : 12 |**** | |
| |
| This better reflects the latency suffered by the application (if it is |
| synchronous I/O), whereas the default mode without kernel queueing better |
| reflects the performance of the device. |
| |
| Note that the storage device (and storage device controller) usually have |
| queues of their own, which are always included in the latency, with or |
| without -Q. |
| |
| |
| The -D option will print a histogram per disk. Eg: |
| |
| # ./biolatency -D |
| Tracing block device I/O... Hit Ctrl-C to end. |
| ^C |
| |
| Bucket disk = 'xvdb' |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 1 | | |
| 256 -> 511 : 33 |********************** | |
| 512 -> 1023 : 36 |************************ | |
| 1024 -> 2047 : 58 |****************************************| |
| 2048 -> 4095 : 51 |*********************************** | |
| 4096 -> 8191 : 21 |************** | |
| 8192 -> 16383 : 2 |* | |
| |
| Bucket disk = 'xvdc' |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 1 | | |
| 256 -> 511 : 38 |*********************** | |
| 512 -> 1023 : 42 |************************* | |
| 1024 -> 2047 : 66 |****************************************| |
| 2048 -> 4095 : 40 |************************ | |
| 4096 -> 8191 : 14 |******** | |
| |
| Bucket disk = 'xvda1' |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 0 | | |
| 256 -> 511 : 18 |********** | |
| 512 -> 1023 : 67 |************************************* | |
| 1024 -> 2047 : 35 |******************* | |
| 2048 -> 4095 : 71 |****************************************| |
| 4096 -> 8191 : 65 |************************************ | |
| 8192 -> 16383 : 65 |************************************ | |
| 16384 -> 32767 : 20 |*********** | |
| 32768 -> 65535 : 7 |*** | |
| |
| This output sows that xvda1 has much higher latency, usually between 0.5 ms |
| and 32 ms, whereas xvdc is usually between 0.2 ms and 4 ms. |
| |
| |
| The -F option prints a separate histogram for each unique set of request |
| flags. For example: |
| |
| ./biolatency.py -Fm |
| Tracing block device I/O... Hit Ctrl-C to end. |
| ^C |
| |
| flags = Read |
| msecs : count distribution |
| 0 -> 1 : 180 |************* | |
| 2 -> 3 : 519 |****************************************| |
| 4 -> 7 : 60 |**** | |
| 8 -> 15 : 123 |********* | |
| 16 -> 31 : 68 |***** | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 2 | | |
| 128 -> 255 : 12 | | |
| 256 -> 511 : 0 | | |
| 512 -> 1023 : 1 | | |
| |
| flags = Sync-Write |
| msecs : count distribution |
| 0 -> 1 : 5 |****************************************| |
| |
| flags = Flush |
| msecs : count distribution |
| 0 -> 1 : 2 |****************************************| |
| |
| flags = Metadata-Read |
| msecs : count distribution |
| 0 -> 1 : 3 |****************************************| |
| 2 -> 3 : 2 |************************** | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 1 |************* | |
| 16 -> 31 : 1 |************* | |
| |
| flags = Write |
| msecs : count distribution |
| 0 -> 1 : 103 |******************************* | |
| 2 -> 3 : 106 |******************************** | |
| 4 -> 7 : 130 |****************************************| |
| 8 -> 15 : 79 |************************ | |
| 16 -> 31 : 5 |* | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 0 | | |
| 256 -> 511 : 1 | | |
| |
| flags = NoMerge-Read |
| msecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 5 |****************************************| |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 1 |******** | |
| |
| flags = NoMerge-Write |
| msecs : count distribution |
| 0 -> 1 : 30 |** | |
| 2 -> 3 : 293 |******************** | |
| 4 -> 7 : 564 |****************************************| |
| 8 -> 15 : 463 |******************************** | |
| 16 -> 31 : 21 |* | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 0 | | |
| 256 -> 511 : 5 | | |
| |
| flags = Priority-Metadata-Read |
| msecs : count distribution |
| 0 -> 1 : 1 |****************************************| |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 1 |****************************************| |
| 8 -> 15 : 1 |****************************************| |
| |
| flags = ForcedUnitAccess-Metadata-Sync-Write |
| msecs : count distribution |
| 0 -> 1 : 2 |****************************************| |
| |
| flags = ReadAhead-Read |
| msecs : count distribution |
| 0 -> 1 : 15 |*************************** | |
| 2 -> 3 : 22 |****************************************| |
| 4 -> 7 : 14 |************************* | |
| 8 -> 15 : 8 |************** | |
| 16 -> 31 : 1 |* | |
| |
| flags = Priority-Metadata-Write |
| msecs : count distribution |
| 0 -> 1 : 9 |****************************************| |
| |
| These can be handled differently by the storage device, and this mode lets us |
| examine their performance in isolation. |
| |
| |
| The -e option shows extension summary(total, average) |
| For example: |
| # ./biolatency.py -e |
| ^C |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 4 |*********** | |
| 128 -> 255 : 2 |***** | |
| 256 -> 511 : 4 |*********** | |
| 512 -> 1023 : 14 |****************************************| |
| 1024 -> 2047 : 0 | | |
| 2048 -> 4095 : 1 |** | |
| |
| avg = 663 usecs, total: 16575 usecs, count: 25 |
| |
| Sometimes 512 -> 1023 usecs is not enough for throughput tuning. |
| Especially a little difference in performance downgrade. |
| By this extension, we know the value in log2 range is about 663 usecs. |
| |
| |
| The -j option prints a dictionary of the histogram. |
| For example: |
| |
| # ./biolatency.py -j |
| ^C |
| {'ts': '2020-12-30 14:33:03', 'val_type': 'usecs', 'data': [{'interval-start': 0, 'interval-end': 1, 'count': 0}, {'interval-start': 2, 'interval-end': 3, 'count': 0}, {'interval-start': 4, 'interval-end': 7, 'count': 0}, {'interval-start': 8, 'interval-end': 15, 'count': 0}, {'interval-start': 16, 'interval-end': 31, 'count': 0}, {'interval-start': 32, 'interval-end': 63, 'count': 2}, {'interval-start': 64, 'interval-end': 127, 'count': 75}, {'interval-start': 128, 'interval-end': 255, 'count': 7}, {'interval-start': 256, 'interval-end': 511, 'count': 0}, {'interval-start': 512, 'interval-end': 1023, 'count': 6}, {'interval-start': 1024, 'interval-end': 2047, 'count': 3}, {'interval-start': 2048, 'interval-end': 4095, 'count': 31}]} |
| |
| the key `data` is the list of the log2 histogram intervals. The `interval-start` and `interval-end` define the |
| latency bucket and `count` is the number of I/O's that lie in that latency range. |
| |
| # ./biolatency.py -jF |
| ^C |
| {'ts': '2020-12-30 14:37:59', 'val_type': 'usecs', 'data': [{'interval-start': 0, 'interval-end': 1, 'count': 0}, {'interval-start': 2, 'interval-end': 3, 'count': 0}, {'interval-start': 4, 'interval-end': 7, 'count': 0}, {'interval-start': 8, 'interval-end': 15, 'count': 0}, {'interval-start': 16, 'interval-end': 31, 'count': 1}, {'interval-start': 32, 'interval-end': 63, 'count': 1}, {'interval-start': 64, 'interval-end': 127, 'count': 0}, {'interval-start': 128, 'interval-end': 255, 'count': 0}, {'interval-start': 256, 'interval-end': 511, 'count': 0}, {'interval-start': 512, 'interval-end': 1023, 'count': 0}, {'interval-start': 1024, 'interval-end': 2047, 'count': 2}], 'flags': 'Sync-Write'} |
| {'ts': '2020-12-30 14:37:59', 'val_type': 'usecs', 'data': [{'interval-start': 0, 'interval-end': 1, 'count': 0}, {'interval-start': 2, 'interval-end': 3, 'count': 0}, {'interval-start': 4, 'interval-end': 7, 'count': 0}, {'interval-start': 8, 'interval-end': 15, 'count': 0}, {'interval-start': 16, 'interval-end': 31, 'count': 0}, {'interval-start': 32, 'interval-end': 63, 'count': 0}, {'interval-start': 64, 'interval-end': 127, 'count': 0}, {'interval-start': 128, 'interval-end': 255, 'count': 2}, {'interval-start': 256, 'interval-end': 511, 'count': 0}, {'interval-start': 512, 'interval-end': 1023, 'count': 2}, {'interval-start': 1024, 'interval-end': 2047, 'count': 1}], 'flags': 'Unknown'} |
| {'ts': '2020-12-30 14:37:59', 'val_type': 'usecs', 'data': [{'interval-start': 0, 'interval-end': 1, 'count': 0}, {'interval-start': 2, 'interval-end': 3, 'count': 0}, {'interval-start': 4, 'interval-end': 7, 'count': 0}, {'interval-start': 8, 'interval-end': 15, 'count': 0}, {'interval-start': 16, 'interval-end': 31, 'count': 0}, {'interval-start': 32, 'interval-end': 63, 'count': 0}, {'interval-start': 64, 'interval-end': 127, 'count': 0}, {'interval-start': 128, 'interval-end': 255, 'count': 0}, {'interval-start': 256, 'interval-end': 511, 'count': 0}, {'interval-start': 512, 'interval-end': 1023, 'count': 0}, {'interval-start': 1024, 'interval-end': 2047, 'count': 1}], 'flags': 'Write'} |
| {'ts': '2020-12-30 14:37:59', 'val_type': 'usecs', 'data': [{'interval-start': 0, 'interval-end': 1, 'count': 0}, {'interval-start': 2, 'interval-end': 3, 'count': 0}, {'interval-start': 4, 'interval-end': 7, 'count': 0}, {'interval-start': 8, 'interval-end': 15, 'count': 0}, {'interval-start': 16, 'interval-end': 31, 'count': 0}, {'interval-start': 32, 'interval-end': 63, 'count': 0}, {'interval-start': 64, 'interval-end': 127, 'count': 0}, {'interval-start': 128, 'interval-end': 255, 'count': 0}, {'interval-start': 256, 'interval-end': 511, 'count': 0}, {'interval-start': 512, 'interval-end': 1023, 'count': 4}], 'flags': 'Flush'} |
| |
| The -j option used with -F prints a histogram dictionary per set of I/O flags. |
| |
| # ./biolatency.py -jD |
| ^C |
| {'ts': '2020-12-30 14:40:00', 'val_type': 'usecs', 'data': [{'interval-start': 0, 'interval-end': 1, 'count': 0}, {'interval-start': 2, 'interval-end': 3, 'count': 0}, {'interval-start': 4, 'interval-end': 7, 'count': 0}, {'interval-start': 8, 'interval-end': 15, 'count': 0}, {'interval-start': 16, 'interval-end': 31, 'count': 0}, {'interval-start': 32, 'interval-end': 63, 'count': 1}, {'interval-start': 64, 'interval-end': 127, 'count': 1}, {'interval-start': 128, 'interval-end': 255, 'count': 1}, {'interval-start': 256, 'interval-end': 511, 'count': 1}, {'interval-start': 512, 'interval-end': 1023, 'count': 6}, {'interval-start': 1024, 'interval-end': 2047, 'count': 1}, {'interval-start': 2048, 'interval-end': 4095, 'count': 3}], 'Bucket ptr': b'sda'} |
| |
| The -j option used with -D prints a histogram dictionary per disk device. |
| |
| # ./biolatency.py -jm |
| ^C |
| {'ts': '2020-12-30 14:42:03', 'val_type': 'msecs', 'data': [{'interval-start': 0, 'interval-end': 1, 'count': 11}, {'interval-start': 2, 'interval-end': 3, 'count': 3}]} |
| |
| The -j with -m prints a millisecond histogram dictionary. The `value_type` key is set to msecs. |
| |
| USAGE message: |
| |
| # ./biolatency -h |
| usage: biolatency.py [-h] [-T] [-Q] [-m] [-D] [-F] [-e] [-j] [-d DISK] |
| [interval] [count] |
| |
| Summarize block device I/O latency as a histogram |
| |
| positional arguments: |
| interval output interval, in seconds |
| count number of outputs |
| |
| optional arguments: |
| -h, --help show this help message and exit |
| -T, --timestamp include timestamp on output |
| -Q, --queued include OS queued time in I/O time |
| -m, --milliseconds millisecond histogram |
| -D, --disks print a histogram per disk device |
| -F, --flags print a histogram per set of I/O flags |
| -e, --extension summarize average/total value |
| -j, --json json output |
| -d DISK, --disk DISK Trace this disk only |
| |
| examples: |
| ./biolatency # summarize block I/O latency as a histogram |
| ./biolatency 1 10 # print 1 second summaries, 10 times |
| ./biolatency -mT 1 # 1s summaries, milliseconds, and timestamps |
| ./biolatency -Q # include OS queued time in I/O time |
| ./biolatency -D # show each disk device separately |
| ./biolatency -F # show I/O flags separately |
| ./biolatency -j # print a dictionary |
| ./biolatency -e # show extension summary(total, average) |
| ./biolatency -d sdc # Trace sdc only |
