88 lines
2.4 KiB
Groff
88 lines
2.4 KiB
Groff
.TH biosnoop 8 "2015-09-16" "USER COMMANDS"
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.SH NAME
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biosnoop \- Trace block device I/O and print details incl. issuing PID.
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.SH SYNOPSIS
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.B biosnoop [\-hQ]
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.SH DESCRIPTION
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This tools traces block device I/O (disk I/O), and prints a one-line summary
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for each I/O showing various details. These include the latency from the time of
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issue to the device to its completion, and the PID and process name from when
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the I/O was first created (which usually identifies the responsible process).
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This uses in-kernel eBPF maps to cache process details (PID and comm) by I/O
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request, as well as a starting timestamp for calculating I/O latency.
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This works by tracing various kernel blk_*() functions using dynamic tracing,
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and will need updating to match any changes to these functions.
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This makes use of a Linux 4.4 feature (bpf_perf_event_output());
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for kernels older than 4.4, see the version under tools/old,
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which uses an older mechanism
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Since this uses BPF, only the root user can use this tool.
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.SH REQUIREMENTS
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CONFIG_BPF and bcc.
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.SH OPTIONS
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.TP
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\-h
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Print usage message.
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.TP
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\-Q
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Include a column showing the time spent quueued in the OS.
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.SH EXAMPLES
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.TP
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Trace all block device I/O and print a summary line per I/O:
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#
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.B biosnoop
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.SH FIELDS
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.TP
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TIME(s)
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Time of the I/O completion, in seconds since the first I/O was seen.
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.TP
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COMM
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Cached process name, if present. This usually (but isn't guaranteed) to identify
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the responsible process for the I/O.
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.TP
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PID
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Cached process ID, if present. This usually (but isn't guaranteed) to identify
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the responsible process for the I/O.
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.TP
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DISK
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Disk device name.
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.TP
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T
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Type of I/O: R = read, W = write. This is a simplification.
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.TP
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SECTOR
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Device sector for the I/O.
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.TP
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BYTES
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Size of the I/O, in bytes.
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.TP
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QUE(ms)
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Time the I/O was queued in the OS before being issued to the device,
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in milliseconds.
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.TP
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LAT(ms)
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Time for the I/O (latency) from the issue to the device, to its completion,
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in milliseconds.
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.SH OVERHEAD
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Since block device I/O usually has a relatively low frequency (< 10,000/s),
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the overhead for this tool is expected to be negligible. For high IOPS storage
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systems, test and quantify before use.
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.SH SOURCE
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This is from bcc.
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.IP
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https://github.com/iovisor/bcc
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.PP
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Also look in the bcc distribution for a companion _examples.txt file containing
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example usage, output, and commentary for this tool.
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.SH OS
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Linux
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.SH STABILITY
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Unstable - in development.
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.SH AUTHOR
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Brendan Gregg
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.SH SEE ALSO
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disksnoop(8), iostat(1)
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