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    SubjectRe: [SCHED] wrong priority calc - SIMPLE test case
    On Fri, 13 Jan 2006 12:13:11 +1100
    Con Kolivas <kernel@kolivas.org> wrote:

    > Can you try the following patch on 2.6.15 please? I'm interested in how
    > adversely this affects interactive performance as well as whether it helps
    > your test case.

    "./a.out 5000 & ./a.out 5237 & ./a.out 5331 &"
    "mount space/; sync; sleep 1; time dd if=space/bigfile of=/dev/null
    bs=1M count=256; umount space/"

    PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
    5445 paolo 16 0 2396 288 228 R 34.8 0.1 0:05.84 a.out
    5446 paolo 15 0 2396 288 228 S 32.8 0.1 0:05.53 a.out
    5444 paolo 16 0 2392 288 228 R 31.3 0.1 0:05.99 a.out
    5443 paolo 16 0 10416 1104 848 R 0.2 0.2 0:00.01 top
    5451 paolo 15 0 4948 1468 372 D 0.2 0.3 0:00.01 dd

    DD test takes ~20 s (instead of 8s).

    As you can see DD priority is now very good (15) but it still suffers
    because also my test programs get good priority (15/16).


    Things are BETTER on the real test case (transcode): this is because
    transcode usually gets priority 16 and "dd" gets 15... so dd is quite
    happy.

    BUT what is STRANGE is this: usually transcode is stuck to priority 16
    using about 88% of the CPU, but sometimes (don't know how to reproduce
    it) its priority grows up to 25 and then stay to 25.

    When transcode priority is 25 the DD test is obviously happy: in
    particular 2 things can happen (this is expected because I've observed
    this thing before):

    1) priority of transcode stay to 25 (when the file transcode is
    reading from, through pipes, IS cached).

    2) CPU usage and priority of transcode go down (the file transcode is
    reading from ISN'T cached and DD massive disk usage interferes with
    this reading). When DD finish trancode priority go back to 25.

    --
    Paolo Ornati
    Linux 2.6.15-kolivasPatch on x86_64
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