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.TH biolatency-nd 8 "2015-01-30" "USER COMMANDS" .SH NAME biolatency-nd \- Measure block I/O latency distribution. Uses Linux SystemTap (non-debuginfo). .SH SYNOPSIS .B biolatency-nd.stp [interval [count]] .SH DESCRIPTION This measures block I/O latency (storage I/O, ie, disk I/O), and shows the distribution as a histogram. This can be useful to identify the characteristics of I/O latency, beyond the averages shown by iostat(1). For example, to study I/O latency outliers, or multi-modal distributions. This script uses the kernel tracepoints block_rq_issue and block_rq_complete, to trace the time from storage request to completion. To include extra time spent queued in the kernel, change block_rq_issue to block_rq_insert. .SH REQUIREMENTS SystemTap. .SH OPTIONS .TP interval Interval for reports, in seconds. .TP count Number of reports to output. .SH EXAMPLES .TP Measure block I/O latency, and show a distribution histogram on Ctrl-C: # .B biolatency-nd.stp .TP Measure block I/O latency, and show a report every second, five times: # .B biolatency-nd.stp 1 5 .SH FIELDS .TP value The minimum value, in nanoseconds, for this histogram bucket. Read this value as "I/O latency was at least xxx". .TP count How many I/O fell into this latency range. .SH OVERHEAD Should be low, relative to the rate of disk I/O. Test first. .SH SOURCE This is from the SystemTap lwtools collection. .IP https://github.com/brendangregg/systemtap-lwtools .PP Also look under the examples directory for a text file containing example usage, output, and commentary for this tool. .SH OS Linux .SH STABILITY Unstable - in development. .SH AUTHOR Brendan Gregg .SH SEE ALSO iostat(1)