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    Subject2.2.0-pre[56] swap performance poor with > 1 thrashing task

    On 7 Jan 1999, Zlatko Calusic wrote:

    > 2.2.0-pre5 works very good, indeed, but it still has some not
    > sufficiently explored nuisances:
    >
    > 1) Swap performance in pre-5 is much worse compared to pre-4 in
    > *certain* circumstances. I'm using quite stupid and unintelligent
    > program to check for raw swap speed (attached below). With 64 MB of
    > RAM I usually run it as 'hogmem 100 3' and watch for result which is
    > recently around 6 MB/sec. But when I lately decided to start two
    > instances of it like "hogmem 50 3 & hogmem 50 3 &" in pre-4 I got 2 x
    > 2.5 MB/sec and in pre-5 it is only 2 x 1 MB/sec and disk is making
    > very weird and frightening sounds. My conclusion is that now (pre-5)
    > system behaves much poorer when we have more than one thrashing
    > task. *Please*, check this, it is a quite serious problem.

    I just tried this on 2.2.0-pre6 PentiumII 412Mhz, 128MB SDRAM, one IDE
    disk (/ & swap).

    ./hogmem 100 3 (no swapping)
    Memory speed: 167.60 MB/sec

    ./hogmem 200 3
    Memory speed: 9.01 MB/sec

    ./hogmem 100 3 & ./hogmem 100 3
    Memory speed: 0.96 MB/sec
    Memory speed: 0.96 MB/sec

    ./hogmem 100 3 (no swap)
    Memory speed: 180.18 MB/sec

    ./hogmem 200 3
    Memory speed: 8.68 MB/sec

    I then tried

    ./hogmem 200 3 &

    find / (on about 1.5GB of data on ext2 and vfat and nfs repeatedly)

    And launched netscape. After 45 mins, I didn't restart the find, and
    about 3 mins later the hogmem completed at 0.75MB/sec. Netscape was
    surprisingly responsive however.

    Dax Kelson




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