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What meaning do the following bootchart statistics have?

Screenshot

  1. CPU (user + sys) - show percentage of usage all cores of my CPU?
  2. I/O(wait) something wait input-output? What does it mean?
  3. Disk throughput and Disk utilization - what difference between them?
  4. Unint.sleep - ???
  5. Sleepeng - process, that doesn't use CPU time?
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As stated in the Boot chart Documentation, the data collection process uses:

/proc/stat          system-wide CPU statistics: user, system, IO and idle times
/proc/diskstats     system-wide disk statistics: disk utilization and throughput
/proc/[PID]/stat    information about the running processes: start time, parent PID, process state, CPU usage, etc.

Therefore,

  1. Yes

  2. These are CPU cycles wasted waiting for I/O

  3. a. The disk throughput is a number in MBps/sec measuring the data that gets read/written to/from the disk.

    b. The Disk utilization is a % between 0 (meaning idle) and 100 (meaning fully occupied)

  4. "Unint. sleep" is the abbreviation of "Uninterrupted sleep" (See 2. above)

  5. "Sleeping" means "not doing anything" which would be not very good while performing a boot... (Also see 2. above)

A simple example:

Let's suppose you do video conversion: you will read very little disk, but use 100% of 1 CPU, then the Disk Utilisation will be 1% and the total CPU on a dual-Core CPU will be 50%

Now you do a file copy: 1 CPU will be at 1% and the Disk Utilisation will be at 40%; now you do 2 file copies at the same time: CPU will be at 2% and Disk Utilisation will be at 80%.

If you do a third file copy at the same time, Disk Utilisation will be at 100%, but CPU% will go up and show 20% "I/O Wait": it doesn't go any faster: the CPU is just waiting until it can push some more data to the disk.

This is just an example: the % depend on the availability of RAM, CPU and the speed of your disk!

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    Thanks, @Fabby please explain The Disk utilization is a % between 0 (meaning idle) and 100 (meaning fully occupied) in more details.
    – igor_rb
    Jan 19, 2015 at 7:28

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