NAME

       funcslower - Trace slow kernel or user function calls.

SYNOPSIS

       funcslower  [-hf]  [-p  PID]  [-U  |  -K]  [-m MIN_MS] [-u MIN_US] [-a ARGUMENTS] [-T] [-t] [-v] function
       [function ...]

DESCRIPTION

       This script traces a kernel or user function's entry and return points, and prints  a  message  when  the
       function's  latency  exceeded the specified threshold.  Multiple functions are supported, and you can mix
       kernel functions with user functions in different libraries.

       WARNING: See the OVERHEAD section.

       By default, a minimum millisecond threshold of 1 is used. Recursive functions are not supported: only the
       inner-most recursive invocation will be traced.

       Since this uses BPF, only the root user can use this tool.

REQUIREMENTS

       CONFIG_BPF and bcc.

OPTIONS

       -p PID Trace this PID only.

       -m MIN_NS
              Minimum duration to trace, in milliseconds. Default is 1 ms.

       -u MIN_US
              Minimum duration to trace, in microseconds.

       -a ARGUMENTS
              Print the function's arguments, up to 6.

       -T     Print a HH:MM:SS timestamp with each entry.

       -t     Print a seconds timestamp with each entry, at microsecond resolution.

       -f     Print output in folded stack format.

       -U     Show stacks from user space only (no kernel space stacks).

       -K     Show stacks from kernel space only (no user space stacks).

       -v     Print the resulting BPF program, for debugging purposes.

       function
              The  function  to trace -- multiple functions are supported. If a plain function name is provided,
              the function is assumed to be a kernel function. For user functions, provide the library name  and
              the function name, e.g. bash:readline or c:malloc.

EXAMPLES

       Trace vfs_write calls slower than 1ms:
              # funcslower vfs_write

       Trace open() calls in libc slower than 10us:
              # funcslower -u 10 c:open

       Trace both malloc() and free() slower than 10us, in pid 135 only:
              # funcslower -p 135 -u 10 c:malloc c:free

       Trace the write syscall and print its first 4 arguments:
              # funcslower -a 4 SyS_write

       Trace opens from libc and print the user and kernel stack frames:
              # funcslower -UK c:open

FIELDS

       TIME   Time  of  the event as a human-readable HH:MM:SS format, or a timestamp in seconds at microsecond-
              accuracy from the first event seen.

       COMM   Process name.

       PID    Process ID.

       LAT    Latency of the operation in either microseconds (us) or milliseconds (ms).

       RVAL   The return value from the function. Often useful for diagnosing a relationship  between  slow  and
              failed function calls.

       FUNC   The function name, followed by its arguments if requested.

OVERHEAD

       Depending  on  the  function(s)  being  traced, overhead can become severe. For example, tracing a common
       function like malloc() can slow down a C/C++ program by a factor of 2 or more. On the other hand, tracing
       a  low-frequency  event like the SyS_setreuid() function will probably not be as prohibitive, and in fact
       negligible for functions that are called up to 100-1000 times per second.

       You should first use the funclatency and argdist tools for investigation, because they summarize data in-
       kernel  and  have  a  much  lower overhead than this tool. To get a general idea of the number of times a
       particular function is called (and estimate the overhead), use the funccount tool, e.g.:

       # funccount c:open

SOURCE

       This is from bcc.

              https://github.com/iovisor/bcc

       Also look in the bcc distribution for a companion _examples.txt file containing  example  usage,  output,
       and commentary for this tool.

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Sasha Goldshtein

SEE ALSO

       funccount(8), funclatency(8), argdist(8), trace(8)