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)