1syncsnoop(8) System Manager's Manual syncsnoop(8)
2
3
4
6 syncsnoop - Trace sync() syscall. Uses Linux eBPF/bcc.
7
9 syncsnoop
10
12 syncsnoop traces calls to sync(), which flushes file system buffers to
13 storage devices. These calls can cause performance perturbations, and
14 it can be useful to know if they are happening and how frequently.
15
16 This works by tracing the kernel sys_sync() function using dynamic
17 tracing, and will need updating to match any changes to this function.
18
19 This makes use of a Linux 4.5 feature (bpf_perf_event_output()); for
20 kernels older than 4.5, see the version under tools/old, which uses an
21 older mechanism.
22
23 This program is also a basic example of eBPF/bcc.
24
25 Since this uses BPF, only the root user can use this tool.
26
28 CONFIG_BPF and bcc.
29
31 Trace calls to sync():
32 # syncsnoop
33
35 TIME(s)
36 Time of the call, in seconds.
37
38 CALL Call traced.
39
41 This traces the kernel sync function and prints output for each event.
42 As the rate of this is generally expected to be low (<< 100/s), the
43 overhead is also expected to be negligible.
44
46 This is from bcc.
47
48 https://github.com/iovisor/bcc
49
50 Also look in the bcc distribution for a companion _examples.txt file
51 containing example usage, output, and commentary for this tool.
52
54 Linux
55
57 Unstable - in development.
58
60 Brendan Gregg
61
63 iostat(1)
64
65
66
67USER COMMANDS 2015-08-18 syncsnoop(8)