| Demonstrations of runqlat, the Linux eBPF/bcc version. |
| |
| |
| This program summarizes scheduler run queue latency as a histogram, showing |
| how long tasks spent waiting their turn to run on-CPU. |
| |
| Here is a heavily loaded system: |
| |
| # ./runqlat |
| Tracing run queue latency... Hit Ctrl-C to end. |
| ^C |
| usecs : count distribution |
| 0 -> 1 : 233 |*********** | |
| 2 -> 3 : 742 |************************************ | |
| 4 -> 7 : 203 |********** | |
| 8 -> 15 : 173 |******** | |
| 16 -> 31 : 24 |* | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 30 |* | |
| 128 -> 255 : 6 | | |
| 256 -> 511 : 3 | | |
| 512 -> 1023 : 5 | | |
| 1024 -> 2047 : 27 |* | |
| 2048 -> 4095 : 30 |* | |
| 4096 -> 8191 : 20 | | |
| 8192 -> 16383 : 29 |* | |
| 16384 -> 32767 : 809 |****************************************| |
| 32768 -> 65535 : 64 |*** | |
| |
| The distribution is bimodal, with one mode between 0 and 15 microseconds, |
| and another between 16 and 65 milliseconds. These modes are visible as the |
| spikes in the ASCII distribution (which is merely a visual representation |
| of the "count" column). As an example of reading one line: 809 events fell |
| into the 16384 to 32767 microsecond range (16 to 32 ms) while tracing. |
| |
| I would expect the two modes to be due the workload: 16 hot CPU-bound threads, |
| and many other mostly idle threads doing occasional work. I suspect the mostly |
| idle threads will run with a higher priority when they wake up, and are |
| the reason for the low latency mode. The high latency mode will be the |
| CPU-bound threads. More analysis with this and other tools can confirm. |
| |
| |
| A -m option can be used to show milliseconds instead, as well as an interval |
| and a count. For example, showing three x five second summary in milliseconds: |
| |
| # ./runqlat -m 5 3 |
| Tracing run queue latency... Hit Ctrl-C to end. |
| |
| msecs : count distribution |
| 0 -> 1 : 3818 |****************************************| |
| 2 -> 3 : 39 | | |
| 4 -> 7 : 39 | | |
| 8 -> 15 : 62 | | |
| 16 -> 31 : 2214 |*********************** | |
| 32 -> 63 : 226 |** | |
| |
| msecs : count distribution |
| 0 -> 1 : 3775 |****************************************| |
| 2 -> 3 : 52 | | |
| 4 -> 7 : 37 | | |
| 8 -> 15 : 65 | | |
| 16 -> 31 : 2230 |*********************** | |
| 32 -> 63 : 212 |** | |
| |
| msecs : count distribution |
| 0 -> 1 : 3816 |****************************************| |
| 2 -> 3 : 49 | | |
| 4 -> 7 : 40 | | |
| 8 -> 15 : 53 | | |
| 16 -> 31 : 2228 |*********************** | |
| 32 -> 63 : 221 |** | |
| |
| This shows a similar distribution across the three summaries. |
| |
| |
| A -p option can be used to show one PID only, which is filtered in kernel for |
| efficiency. For example, PID 4505, and one second summaries: |
| |
| # ./runqlat -mp 4505 1 |
| Tracing run queue latency... Hit Ctrl-C to end. |
| |
| msecs : count distribution |
| 0 -> 1 : 1 |* | |
| 2 -> 3 : 2 |*** | |
| 4 -> 7 : 1 |* | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 25 |****************************************| |
| 32 -> 63 : 3 |**** | |
| |
| msecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 2 |** | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 1 |* | |
| 16 -> 31 : 30 |****************************************| |
| 32 -> 63 : 1 |* | |
| |
| msecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 28 |****************************************| |
| 32 -> 63 : 2 |** | |
| |
| msecs : count distribution |
| 0 -> 1 : 1 |* | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 27 |****************************************| |
| 32 -> 63 : 4 |***** | |
| [...] |
| |
| For comparison, here is pidstat(1) for that process: |
| |
| # pidstat -p 4505 1 |
| Linux 4.4.0-virtual (bgregg-xxxxxxxx) 02/08/2016 _x86_64_ (8 CPU) |
| |
| 08:56:11 AM UID PID %usr %system %guest %CPU CPU Command |
| 08:56:12 AM 0 4505 9.00 3.00 0.00 12.00 0 bash |
| 08:56:13 AM 0 4505 7.00 5.00 0.00 12.00 0 bash |
| 08:56:14 AM 0 4505 10.00 2.00 0.00 12.00 0 bash |
| 08:56:15 AM 0 4505 11.00 2.00 0.00 13.00 0 bash |
| 08:56:16 AM 0 4505 9.00 3.00 0.00 12.00 0 bash |
| [...] |
| |
| This is a synthetic workload that is CPU bound. It's only spending 12% on-CPU |
| each second because of high CPU demand on this server: the remaining time |
| is spent waiting on a run queue, as visualized by runqlat. |
| |
| |
| Here is the same system, but when it is CPU idle: |
| |
| # ./runqlat 5 1 |
| Tracing run queue latency... Hit Ctrl-C to end. |
| |
| usecs : count distribution |
| 0 -> 1 : 2250 |******************************** | |
| 2 -> 3 : 2340 |********************************** | |
| 4 -> 7 : 2746 |****************************************| |
| 8 -> 15 : 418 |****** | |
| 16 -> 31 : 93 |* | |
| 32 -> 63 : 28 | | |
| 64 -> 127 : 119 |* | |
| 128 -> 255 : 9 | | |
| 256 -> 511 : 4 | | |
| 512 -> 1023 : 20 | | |
| 1024 -> 2047 : 22 | | |
| 2048 -> 4095 : 5 | | |
| 4096 -> 8191 : 2 | | |
| |
| Back to a microsecond scale, this time there is little run queue latency past 1 |
| millisecond, as would be expected. |
| |
| |
| Now 16 threads are performing heavy disk I/O: |
| |
| # ./runqlat 5 1 |
| Tracing run queue latency... Hit Ctrl-C to end. |
| |
| usecs : count distribution |
| 0 -> 1 : 204 | | |
| 2 -> 3 : 944 |* | |
| 4 -> 7 : 16315 |********************* | |
| 8 -> 15 : 29897 |****************************************| |
| 16 -> 31 : 1044 |* | |
| 32 -> 63 : 23 | | |
| 64 -> 127 : 128 | | |
| 128 -> 255 : 24 | | |
| 256 -> 511 : 5 | | |
| 512 -> 1023 : 13 | | |
| 1024 -> 2047 : 15 | | |
| 2048 -> 4095 : 13 | | |
| 4096 -> 8191 : 10 | | |
| |
| The distribution hasn't changed too much. While the disks are 100% busy, there |
| is still plenty of CPU headroom, and threads still don't spend much time |
| waiting their turn. |
| |
| |
| A -P option will print a distribution for each PID: |
| |
| # ./runqlat -P |
| Tracing run queue latency... Hit Ctrl-C to end. |
| ^C |
| |
| pid = 0 |
| usecs : count distribution |
| 0 -> 1 : 351 |******************************** | |
| 2 -> 3 : 96 |******** | |
| 4 -> 7 : 437 |****************************************| |
| 8 -> 15 : 12 |* | |
| 16 -> 31 : 10 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 16 |* | |
| 128 -> 255 : 0 | | |
| 256 -> 511 : 0 | | |
| 512 -> 1023 : 0 | | |
| 1024 -> 2047 : 0 | | |
| 2048 -> 4095 : 0 | | |
| 4096 -> 8191 : 0 | | |
| 8192 -> 16383 : 1 | | |
| |
| pid = 12929 |
| usecs : count distribution |
| 0 -> 1 : 1 |****************************************| |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 1 |****************************************| |
| |
| pid = 12930 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 1 |****************************************| |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 1 |****************************************| |
| |
| pid = 12931 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 1 |******************** | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 0 | | |
| 256 -> 511 : 0 | | |
| 512 -> 1023 : 2 |****************************************| |
| |
| pid = 12932 |
| 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 : 0 | | |
| 512 -> 1023 : 1 |****************************************| |
| |
| pid = 7 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 426 |************************************* | |
| 4 -> 7 : 457 |****************************************| |
| 8 -> 15 : 16 |* | |
| |
| pid = 9 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 425 |****************************************| |
| 8 -> 15 : 16 |* | |
| |
| pid = 11 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 10 |****************************************| |
| |
| pid = 14 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 8 |****************************************| |
| 4 -> 7 : 2 |********** | |
| |
| pid = 18 |
| usecs : count distribution |
| 0 -> 1 : 414 |****************************************| |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 20 |* | |
| 8 -> 15 : 8 | | |
| |
| pid = 12928 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 1 |****************************************| |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 1 |****************************************| |
| |
| pid = 1867 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 15 |****************************************| |
| 16 -> 31 : 1 |** | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 4 |********** | |
| |
| pid = 1871 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 2 |****************************************| |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 0 | | |
| 256 -> 511 : 0 | | |
| 512 -> 1023 : 1 |******************** | |
| |
| pid = 1876 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 1 |****************************************| |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 0 | | |
| 256 -> 511 : 1 |****************************************| |
| |
| pid = 1878 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 3 |****************************************| |
| |
| pid = 1880 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 3 |****************************************| |
| |
| pid = 9307 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 1 |****************************************| |
| |
| pid = 1886 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 1 |******************** | |
| 8 -> 15 : 2 |****************************************| |
| |
| pid = 1888 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 3 |****************************************| |
| |
| pid = 3297 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 1 |****************************************| |
| |
| pid = 1892 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 1 |******************** | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 0 | | |
| 256 -> 511 : 0 | | |
| 512 -> 1023 : 2 |****************************************| |
| |
| pid = 7024 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 4 |****************************************| |
| |
| pid = 16468 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 3 |****************************************| |
| |
| pid = 12922 |
| usecs : count distribution |
| 0 -> 1 : 1 |****************************************| |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 1 |****************************************| |
| 16 -> 31 : 1 |****************************************| |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 1 |****************************************| |
| |
| pid = 12923 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 1 |******************** | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 2 |****************************************| |
| 128 -> 255 : 0 | | |
| 256 -> 511 : 0 | | |
| 512 -> 1023 : 1 |******************** | |
| 1024 -> 2047 : 1 |******************** | |
| |
| pid = 12924 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 2 |******************** | |
| 8 -> 15 : 4 |****************************************| |
| 16 -> 31 : 1 |********** | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 0 | | |
| 256 -> 511 : 0 | | |
| 512 -> 1023 : 0 | | |
| 1024 -> 2047 : 1 |********** | |
| |
| pid = 12925 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 1 |****************************************| |
| |
| pid = 12926 |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 1 |****************************************| |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 1 |****************************************| |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 0 | | |
| 256 -> 511 : 0 | | |
| 512 -> 1023 : 1 |****************************************| |
| |
| pid = 12927 |
| usecs : count distribution |
| 0 -> 1 : 1 |****************************************| |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 1 |****************************************| |
| |
| |
| A -L option will print a distribution for each TID: |
| |
| # ./runqlat -L |
| Tracing run queue latency... Hit Ctrl-C to end. |
| ^C |
| |
| tid = 0 |
| usecs : count distribution |
| 0 -> 1 : 593 |**************************** | |
| 2 -> 3 : 829 |****************************************| |
| 4 -> 7 : 300 |************** | |
| 8 -> 15 : 321 |*************** | |
| 16 -> 31 : 132 |****** | |
| 32 -> 63 : 58 |** | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 0 | | |
| 256 -> 511 : 13 | | |
| |
| tid = 7 |
| usecs : count distribution |
| 0 -> 1 : 8 |******** | |
| 2 -> 3 : 19 |******************** | |
| 4 -> 7 : 37 |****************************************| |
| [...] |
| |
| |
| And a --pidnss option (short for PID namespaces) will print for each PID |
| namespace, for analyzing container performance: |
| |
| # ./runqlat --pidnss -m |
| Tracing run queue latency... Hit Ctrl-C to end. |
| ^C |
| |
| pidns = 4026532870 |
| msecs : count distribution |
| 0 -> 1 : 40 |****************************************| |
| 2 -> 3 : 1 |* | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 2 |** | |
| 64 -> 127 : 5 |***** | |
| |
| pidns = 4026532809 |
| msecs : count distribution |
| 0 -> 1 : 67 |****************************************| |
| |
| pidns = 4026532748 |
| msecs : count distribution |
| 0 -> 1 : 63 |****************************************| |
| |
| pidns = 4026532687 |
| msecs : count distribution |
| 0 -> 1 : 7 |****************************************| |
| |
| pidns = 4026532626 |
| msecs : count distribution |
| 0 -> 1 : 45 |****************************************| |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 3 |** | |
| |
| pidns = 4026531836 |
| msecs : count distribution |
| 0 -> 1 : 314 |****************************************| |
| 2 -> 3 : 1 | | |
| 4 -> 7 : 11 |* | |
| 8 -> 15 : 28 |*** | |
| 16 -> 31 : 137 |***************** | |
| 32 -> 63 : 86 |********** | |
| 64 -> 127 : 1 | | |
| |
| pidns = 4026532382 |
| msecs : count distribution |
| 0 -> 1 : 285 |****************************************| |
| 2 -> 3 : 5 | | |
| 4 -> 7 : 16 |** | |
| 8 -> 15 : 9 |* | |
| 16 -> 31 : 69 |********* | |
| 32 -> 63 : 25 |*** | |
| |
| Many of these distributions have two modes: the second, in this case, is |
| caused by capping CPU usage via CPU shares. |
| |
| |
| USAGE message: |
| |
| # ./runqlat -h |
| usage: runqlat.py [-h] [-T] [-m] [-P] [--pidnss] [-L] [-p PID] |
| [interval] [count] |
| |
| Summarize run queue (scheduler) 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 |
| -m, --milliseconds millisecond histogram |
| -P, --pids print a histogram per process ID |
| --pidnss print a histogram per PID namespace |
| -L, --tids print a histogram per thread ID |
| -p PID, --pid PID trace this PID only |
| |
| examples: |
| ./runqlat # summarize run queue latency as a histogram |
| ./runqlat 1 10 # print 1 second summaries, 10 times |
| ./runqlat -mT 1 # 1s summaries, milliseconds, and timestamps |
| ./runqlat -P # show each PID separately |
| ./runqlat -p 185 # trace PID 185 only |
