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• -j2? -j4? (Score:2)

  by jhi (318)

  Just out of curiosity, it would be nice to know whether the traditional wisdom of overcommitting by one processor works (that is, is -j3 really faster than -j2), and also how much overovercommitting (-j4) trashes the systems?
  
  • Re:-j2? -j4? (Score:2)

    by pudge (1) on 2003.09.19 11:07 (#24344) Homepage Journal

    I was kinda wondering the same thing myself ... but it takes so long to do each build, I don't want to spend the time doing the benchmarks! :-)
    
    make -j2, G5:

    real    2m11.921s
    user    3m26.660s
    sys     0m45.240s

    make -j3, G5:

    real    2m13.723s
    user    3m29.480s
    sys     0m49.440s

    make -j4, G5:

    real    2m25.240s
    user    3m31.290s
    sys     0m50.420s

    make -j10, G5:

    real    2m24.177s
    user    3m30.840s
    sys     0m50.500s

    So it actually looks like -j2 is slightly faster. I did both -j2 and -j3 twice, with similar results: -j2 is faster by a good second or two. And I also did -j4 more times, with similar results (slower than -j2 and -j3 by at least several seconds).
    
    One interesting note: Encode is always the last to finish. I wonder if making Encode begin to compile first would speed up the results somewhat. So with this run, I moved lib/auto/Encode/Encode.bundle to the beginning of dynamic_ext in the Makefile after Configure -des, and before make.
    
    make -j2, G5, putting Encode first:

    real    2m12.722s
    user    3m26.750s
    sys     0m47.140s

    make -j3, G5, putting Encode first:

    real    2m13.575s
    user    3m30.260s
    sys     0m48.490s

    Hm. Never mind. In the last test there, Encode STILL finished last, BTW.

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