NAME

       ext4dist - Summarize ext4 operation latency. Uses Linux eBPF/bcc.

SYNOPSIS

       ext4dist [-h] [-T] [-m] [-p PID] [interval] [count]

DESCRIPTION

       This  tool  summarizes  time  (latency)  spent  in common ext4 file operations: reads, writes, opens, and
       syncs, and presents it as a power-of-2 histogram. It uses an in-kernel eBPF map to  store  the  histogram
       for efficiency.

       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

       -h     Print usage message.

       -T     Don't include timestamps on interval output.

       -m     Output in milliseconds.

       -p PID Trace this PID only.

EXAMPLES

       Trace ext4 operation time, and print a summary on Ctrl-C:
              # ext4dist

       Trace PID 181 only:
              # ext4dist -p 181

       Print 1 second summaries, 10 times:
              # ext4dist 1 10

       1 second summaries, printed in milliseconds
              # ext4dist -m 1

FIELDS

       msecs  Range of milliseconds for this bucket.

       usecs  Range of microseconds for this bucket.

       count  Number of operations in this time range.

       distribution
              ASCII representation of the distribution (the count column).

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 may become noticeable.  Measure and quantify before use.

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

       ext4snoop(8)