• 2 replies
  • Latest Post - ‏2012-10-12T18:17:12Z by Mark_Ray_AIX_Perf
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Pinned topic How could i confirm that system is either cpu or memory or I/O bound?

‏2012-08-13T08:26:39Z |
Hello all,

Form the 'vmstat' output, How could I say whether the system is CPU bound or Memory bound or I/O bound?

Any response is appreciated!

Updated on 2012-10-12T18:17:12Z at 2012-10-12T18:17:12Z by Mark_Ray_AIX_Perf
  • Steve_ATS
    43 Posts

    Re: How could i confirm that system is either cpu or memory or I/O bound?

    I would start by reviewing:

    For vmstat, memory bound means "avm" (4K units) is >= 97% of the real memory (vmstat -v) and you are physically paging (pi/po) columns.

    CPU bound means you are out of physical cpus (you need to review entitlement, entitlement consumed) and you have no idle time (there are exceptions to this generalization).

    vmstat alone is not going to tell you if you are I/O bound. Much more complicated. Training here:
  • Mark_Ray_AIX_Perf
    1 Post

    Re: How could i confirm that system is either cpu or memory or I/O bound?

    Use " vmstat " Here's an example:

    lparx:/>vmstat -w 2

    System configuration: lcpu=16 mem=16384MB ent=0.40

    kthr memory page faults cpu

    r b avm fre re pi po fr sr cy in sy cs us sy id wa pc ec
    1 0 2806976 14295 0 0 0 0 0 0 119 1766 1090 1 4 95 0 0.04 9.0
    1 0 2807037 14234 0 0 0 0 0 0 123 4584 1101 4 7 89 0 0.07 18.1
    1 0 2806973 14298 0 0 0 0 0 0 29 555 285 1 5 94 0 0.05 11.5
    2 0 2808770 12501 0 0 0 0 0 0 180 98918 1512 19 35 46 0 0.33 83.1

    To determine if CPUs are being pegged, look at the us, sy and wa columns under the "cpu" heading. These values are
    expressed in percentages of CPU use. Total up the three columns' values. If us+sy+wa ~= 85% or greater, you might
    consider adding CPUs or adjusting your workload.

    For Memory, just look at the fre column under the "memory" heading. fre is short for "free list" and tells you the
    number of 4K memory pages that are available in the system for work assignments. If this value drops close to zero,
    you either need to add more memory or free some up.

    For I/O: look at the wa column under the cpu heading. This stands for "wait", and tells you the amount of time CPUs
    had to hold up their activity while either disk or NFS I/O took place. The higher this number, the more time your
    system spends idle, waiting for I/O to complete. If you see a high number here, use "iostat" to determine where the
    wait is happening: on reads, writes, in queue or a combination of all three.

    Mark Ray
    System P and AIX Performance