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.TH fsslower-nd 8 "2015-01-30" "USER COMMANDS" .SH NAME fsslower-nd \- Trace slow file system sync reads and writes. Uses Linux SystemTap (non-debuginfo). .SH SYNOPSIS .B fsslower-nd.stp [min_ms] .SH DESCRIPTION fsslower-nd.stp dynamically traces two common file system functions: do_sync_read() and do_sync_write(), and shows details of each call that is slower than a threshold. Many, but not all, file systems and workloads use these functions. Tracing their time provides one view of suffered file system latency. Other file system requests not covered by these functions and this tool include: asynchronous I/O, directory operations, and file handle operations. .SH REQUIREMENTS SystemTap. .SH OPTIONS .TP min_ms Minimum millisecond threshold. .SH EXAMPLES .TP Measure (most) file system synchronous read and write requests with latency slower than or equal to 5 ms: # .B fsslower-nd.stp 5 .SH FIELDS .TP TIME Time of the event completion. .TP PID Process ID. .TP COMM Process name. .TP FUNC Kernel function traced. .TP SIZE Size of FS request, in bytes. .TP LAT(ms) Latency of function, in milliseconds. .SH OVERHEAD The overheads are measurable, as file system requests can be very frequent, and the small overhead of tracing each (eg, 4 microseconds per call) can begin to add up. Best case, it won't be noticeable. Worst case, the application may run 2x slower. .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), fslatency-nd.stp(8), biolatency-nd.stp(8)