bcc-gethostlatency(8)

1gethostlatency(8)           System Manager's Manual          gethostlatency(8)
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NAME

6       gethostlatency  -  Show latency for getaddrinfo/gethostbyname[2] calls.
7       Uses Linux eBPF/bcc.
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SYNOPSIS

10       gethostlatency
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DESCRIPTION

13       This traces and prints when getaddrinfo(), gethostbyname(),  and  geth‐
14       ostbyname2() are called, system wide, and shows the responsible PID and
15       command name, latency of the call (duration) in milliseconds,  and  the
16       host string.
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18       This  tool  can  be  useful for identifying DNS latency, by identifying
19       which remote host name lookups were slow, and by how much.
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21       This makes use of a Linux 4.4  feature  (bpf_perf_event_output());  for
22       kernels  older than 4.4, see the version under tools/old, which uses an
23       older mechanism
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25       This tool currently uses dynamic tracing of  user-level  functions  and
26       registers,  and  may need modifications to match your software and pro‐
27       cessor architecture.
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29       Since this uses BPF, only the root user can use this tool.
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REQUIREMENTS

32       CONFIG_BPF and bcc.
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OPTIONS

35       -p PID Trace this process ID only.
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EXAMPLES

38       Trace host lookups (getaddrinfo/gethostbyname[2]) system wide:
39              # gethostlatency
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FIELDS

42       TIME   Time of the command (HH:MM:SS).
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44       PID    Process ID of the client performing the call.
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46       COMM   Process (command) name of the client performing the call.
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48       HOST   Host name string: the target of the lookup.
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OVERHEAD

51       The rate of lookups should be relatively low, so the  overhead  is  not
52       expected to be a problem.
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SOURCE

55       This is from bcc.
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57              https://github.com/iovisor/bcc
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59       Also  look  in  the bcc distribution for a companion _examples.txt file
60       containing example usage, output, and commentary for this tool.
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OS

63       Linux
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STABILITY

66       Unstable - in development.
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AUTHOR

69       Brendan Gregg
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