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160 lines
8.3 KiB
160 lines
8.3 KiB
Demonstrations of nfsdist, the Linux eBPF/bcc version. |
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nfsdist traces NFS reads, writes, opens, and getattr, and summarizes their |
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latency as a power-of-2 histogram. For example: |
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./nfsdist.py |
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Tracing NFS operation latency... Hit Ctrl-C to end. |
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operation = read |
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usecs : count distribution |
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0 -> 1 : 4 | | |
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2 -> 3 : 0 | | |
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4 -> 7 : 0 | | |
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8 -> 15 : 7107 |************** | |
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16 -> 31 : 19864 |****************************************| |
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32 -> 63 : 1494 |*** | |
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64 -> 127 : 491 | | |
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128 -> 255 : 1810 |*** | |
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256 -> 511 : 6356 |************ | |
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512 -> 1023 : 4860 |********* | |
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1024 -> 2047 : 3070 |****** | |
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2048 -> 4095 : 1853 |*** | |
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4096 -> 8191 : 921 |* | |
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8192 -> 16383 : 122 | | |
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16384 -> 32767 : 15 | | |
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32768 -> 65535 : 5 | | |
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65536 -> 131071 : 2 | | |
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131072 -> 262143 : 1 | | |
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operation = write |
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usecs : count distribution |
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0 -> 1 : 0 | | |
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2 -> 3 : 0 | | |
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4 -> 7 : 0 | | |
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8 -> 15 : 1 | | |
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16 -> 31 : 0 | | |
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32 -> 63 : 9 | | |
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64 -> 127 : 19491 |****************************************| |
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128 -> 255 : 3064 |****** | |
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256 -> 511 : 940 |* | |
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512 -> 1023 : 365 | | |
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1024 -> 2047 : 312 | | |
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2048 -> 4095 : 119 | | |
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4096 -> 8191 : 31 | | |
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8192 -> 16383 : 84 | | |
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16384 -> 32767 : 31 | | |
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32768 -> 65535 : 5 | | |
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65536 -> 131071 : 3 | | |
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131072 -> 262143 : 0 | | |
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262144 -> 524287 : 1 | | |
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operation = getattr |
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usecs : count distribution |
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0 -> 1 : 27 |****************************************| |
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2 -> 3 : 2 |** | |
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4 -> 7 : 3 |**** | |
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8 -> 15 : 0 | | |
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16 -> 31 : 0 | | |
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32 -> 63 : 0 | | |
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64 -> 127 : 0 | | |
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128 -> 255 : 0 | | |
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256 -> 511 : 2 |** | |
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512 -> 1023 : 2 |** | |
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operation = open |
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usecs : count distribution |
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0 -> 1 : 0 | | |
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2 -> 3 : 0 | | |
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4 -> 7 : 0 | | |
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8 -> 15 : 0 | | |
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16 -> 31 : 0 | | |
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32 -> 63 : 0 | | |
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64 -> 127 : 0 | | |
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128 -> 255 : 0 | | |
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256 -> 511 : 2 |****************************************| |
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In this example you can see that the read traffic is rather bi-modal, with about |
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26K reads falling within 8 - 30 usecs and about 18K reads spread between 128 - |
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8191 usecs. Write traffic is largely clustered in the 64 - 127 usecs bracket. |
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The faster read traffic is probably coming from a filesystem cache and the slower |
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traffic from disk. The reason why the writes are so consistently fast is because |
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this example test was run on a couple of VM's and I believe the hypervisor was |
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caching all the write traffic to memory. |
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This "latency" is measured from when the operation was issued from the VFS |
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interface to the file system, to when it completed. This spans everything: |
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RPC latency, network latency, file system CPU cycles, file system locks, run |
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queue latency, etc. This is a better measure of the latency suffered by |
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applications reading from a NFS share and can better expose problems |
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experienced by NFS clients. |
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Note that this only traces the common NFS operations (read, write, open and |
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getattr). I chose to include getattr as a significant percentage of NFS |
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traffic end up being getattr calls and are a good indicator of problems |
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with an NFS server. |
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An optional interval and a count can be provided, as well as -m to show the |
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distributions in milliseconds. For example: |
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./nfsdist -m 1 5 |
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Tracing NFS operation latency... Hit Ctrl-C to end. |
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11:02:39: |
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operation = write |
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msecs : count distribution |
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0 -> 1 : 1 | | |
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2 -> 3 : 24 |******** | |
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4 -> 7 : 114 |****************************************| |
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8 -> 15 : 9 |*** | |
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16 -> 31 : 1 | | |
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32 -> 63 : 1 | | |
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11:02:40: |
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operation = write |
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msecs : count distribution |
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0 -> 1 : 0 | | |
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2 -> 3 : 11 |*** | |
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4 -> 7 : 111 |****************************************| |
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8 -> 15 : 13 |**** | |
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16 -> 31 : 1 | | |
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11:02:41: |
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operation = write |
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msecs : count distribution |
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0 -> 1 : 0 | | |
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2 -> 3 : 21 |****** | |
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4 -> 7 : 137 |****************************************| |
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8 -> 15 : 3 | | |
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This shows a write workload, with writes hovering primarily in the 4-7ms range. |
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USAGE message: |
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./nfsdist -h |
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usage: nfsdist.py [-h] [-T] [-m] [-p PID] [interval] [count] |
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Summarize NFS operation latency |
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positional arguments: |
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interval output interval, in seconds |
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count number of outputs |
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optional arguments: |
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-h, --help show this help message and exit |
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-T, --notimestamp don't include timestamp on interval output |
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-m, --milliseconds output in milliseconds |
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-p PID, --pid PID trace this PID only |
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examples: |
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./nfsdist # show operation latency as a histogram |
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./nfsdist -p 181 # trace PID 181 only |
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./nfsdist 1 10 # print 1 second summaries, 10 times |
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./nfsdist -m 5 # 5s summaries, milliseconds
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