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    Subjectptrace performance (was: [Bug #12208] uml is very slow on 2.6.28 host)
    Disclaimer: I'm not using UML, but these problems may be related.

    > Bug-Entry :
    > Subject : uml is very slow on 2.6.28 host
    > Submitter : Miklos Szeredi <>
    > Date : 2008-12-12 9:35 (93 days old)
    > References :

    The other day I noticed a dramatic ptrace slowdown between 2.6.27 and
    2.6.28.x (verified with In particular, a command like

    dd if=/dev/zero of=/dev/null bs=1024k count=1024

    will normally report a throughput in the GB/s range. On 2.6.27, this is
    also true if you run

    strace -o /dev/null <dd command as above>

    which is only a little slower. But if I do the same on 2.6.28.x, I get a
    throughput of about 100 MB/s or less, i.e. less than 10%. I tried the
    commands on three different machines (an Athlon64 3000+, a Core Duo
    T2400 and an Atom 330), and they all behave similar. The more system
    calls a program uses, the worse the slowdown (try the dd command with
    bs=16k and count=65536, for example - but don't hold your breath).

    Interestingly, the CPUs are mostly idle while the command is executing
    on 2.6.28.x, but there is a high (system) load on 2.6.27. Therefore, I
    suspect that it's a scheduling or maybe timer problem that was
    introduced between 2.6.27 and 2.6.28. I haven't had the time to check
    the rc kernels yet; perhaps someone else can run a quick check to verify
    that it's gone in the latest 2.6.29-rc.

    Michael "Tired" Riepe <>
    X-Tired: Each morning I get up I die a little

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