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    Subject[Bug 890] New: performance regression compared to 2.4.20 under tight RAM conditions

    Summary: performance regression compared to 2.4.20 under tight
    RAM conditions
    Kernel Version: 2.5.73
    Status: NEW
    Severity: normal

    debian unstable

    Hardware Environment:
    Pentium III 700Mhz
    I815E Based motherboard
    64MB SDRAM 133
    WD 6GB harddrive, UDMA2

    Software Environment:
    GCC 3.3-2
    glibc 2.3.1-16
    Swap partition 123MB
    Swap file(on ext3 fs) of about 96MB

    Problem Description:

    For quite a time I had the feeling that the 2.5.x kernels perform worse than
    2.4.x on my box, especially when having to do aggrassive swapping(Switching
    between relatively heavyweight(ram wise) applications)

    I considered this feeling subjective at first, however, eventually I took the
    time to write some benchmarking code and compare results.

    The code(attached) is pretty trivial, it forks, mallocs and initialize a very
    large bulk of memory(I used total RAM*1.5), in order to force the system to
    swap, and simulate two processes fighting on RAM space when there is no enough
    of that scared resource:-)

    After both processes end their work, the parent process reports on the total
    running time.

    The code was compiled using gcc 3.3 with -O2 parameter.

    I've done 20 iterations on each of the three kernels:
    Stock debian 2.4.20 (kernel-source-2.4.20-5)
    Stock vanilla 2.5.73 with preempt
    Stock vanilla 2.5.73 without preempt

    Result are at follows:
    2.4.20 : Mean - 14.1732 Max - 16.0875 Min - 12.9977
    2.5.73 : Mean - 17.1692 Max - 21.8161 Min - 15.4827
    2.5.73(w/o prempt): Mean - 16.9054 Max - 19.0174 Min - 15.4137

    As can be seen, the differences are quite significant, about three seconds on
    average, which I believe may be related to the increased swapping time I have

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