NAME

       ext4slower - Trace slow ext4 file operations, with per-event details.

SYNOPSIS

       ext4slower [-h] [-j] [-p PID] [min_ms]

DESCRIPTION

       This tool traces common ext4 file operations: reads, writes, opens, and syncs. It measures the time spent
       in these operations, and prints details for each that exceeded a threshold.

       WARNING: See the OVERHEAD section.

       By default, a minimum millisecond threshold of 10 is used. If a threshold of 0 is used,  all  events  are
       printed (warning: verbose).

       Since  this works by tracing the ext4_file_operations interface functions, it will need updating to match
       any changes to these functions.

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

REQUIREMENTS

       CONFIG_BPF and bcc.

OPTIONS

       -p PID Trace this PID only.

       min_ms Minimum I/O latency (duration) to trace, in milliseconds. Default is 10 ms.

EXAMPLES

       Trace synchronous file reads and writes slower than 10 ms:
              # ext4slower

       Trace slower than 1 ms:
              # ext4slower 1

       Trace slower than 1 ms, and output just the fields in parsable format (csv):
              # ext4slower -j 1

       Trace all file reads and writes (warning: the output will be verbose):
              # ext4slower 0

       Trace slower than 1 ms, for PID 181 only:
              # ext4slower -p 181 1

FIELDS

       TIME(s)
              Time of I/O completion since the first I/O seen, in seconds.

       COMM   Process name.

       PID    Process ID.

       T      Type of operation. R == read, W == write, O == open, S == fsync.

       OFF_KB File offset for the I/O, in Kbytes.

       BYTES  Size of I/O, in bytes.

       LAT(ms)
              Latency (duration) of I/O, measured from when it was issued by VFS to the filesystem, to  when  it
              completed.  This time is inclusive of block device I/O, file system CPU cycles, file system locks,
              run queue latency, etc. It's a more accurate measure  of  the  latency  suffered  by  applications
              performing file system I/O, than to measure this down at the block device interface.

       FILENAME
              A cached kernel file name (comes from dentry->d_iname).

       ENDTIME_us
              Completion timestamp, microseconds (-j only).

       OFFSET_b
              File offset, bytes (-j only).

       LATENCY_us
              Latency (duration) of the I/O, in microseconds (-j only).

OVERHEAD

       This adds low-overhead instrumentation to these ext4 operations, including reads and writes from the file
       system cache. Such reads and writes can be very frequent (depending on  the  workload;  eg,  1M/sec),  at
       which  point  the  overhead  of  this  tool  (even  if  it prints no "slower" events) can begin to become
       significant. Measure and quantify before use. If this continues to be a problem, consider switching to  a
       tool that prints in-kernel summaries only.

       Note  that  the  overhead  of  this  tool  should  be  less than fileslower(8), as this tool targets ext4
       functions only, and not all file read/write paths (which can include socket I/O).

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

       Brendan Gregg

SEE ALSO

       biosnoop(8), funccount(8), fileslower(8)