make -jX build(world|kernel): test results

Tillman Hodgson tillman at
Wed Jan 14 19:32:54 PST 2004


Occasionally the question pops up on the questions@ list about what the
fastest -jX number is for a single CPU system. I had some spare time so
I tried out a small matrix of possibilities.

My conclusion is that using -jX at all is mostly a waste of time on
single CPU systems running -STABLE (even with multiple spindles being
involved), especially when one considers that -jX may introduce build


* I used the simple shell "time" command
* /usr/obj was cleaned out before each run and I waited at least 30
  seconds afterwards for write caching to settle down
* This is my regular build host for my network
* I built 4 kernels: 3 customized and GENERIC (see above for why)
* Celeron 900, 256Mb of RAM, /usr/src and /usr/obj are both on their own
  set of spindles
    * /usr/obj consumes part of a vinum mirror on dual 40Gb 7200RPM
      Maxtor 6L040J2's (the remaining vinum filesystems weren't active
      during this test)
    * /usr/src is on a 2,1Gb Compaq ST32550N SCSI-2 drive
    * The operating system is on separate spindles


       buildworld   -j2 buildworld   -j3 buildworld   -j4 buildworld
       ==========   ==============   ==============   ==============
real   57m10.367s   54m10.992s       55m7.494s        55m1.459s
user   38m5.436s    38m20.852s       38m22.453s       38m23.056s
sys    9m2.801s     10m12.876s       10m17.140s       10m14.792s

       buildkernel  -j2 buildkernel  -j3 buildkernel  -j4 buildkernel
       ===========  ===============  ===============  ===============
real   36m59.994s   36m58.988s       37m42.956s       37m31.627s
user   29m35.597s   29m43.405s       29m43.846s       29m48.652s
sys    4m50.478s    5m26.372s        5m26.883s        5m22.763s

Thought this might be of some interest,


Re: alt.sysadmin.recovery
A fitting punishment for kindly naivete, to end up belonging here. 
    - A.S.R. quote (Chris Johnson)
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