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    SubjectRe: md mirror / ext3 / dual core performance strange phenomenon?
    Date
    Erik Slagter (on Mon, 14 Aug 2006 15:12:14 +0200) wrote:
    >Now, what puzzles me, is that compiling the kernel (2.6.17.7) using
    >either "make -j1 ..." or "make -j2 ..." or "make -j3 ..." makes the
    >building take about 6.5 minutes, which is really dissatisfying for this
    >cpu/harddisks combination. Also, top shows that most of the time both
    >core are between 10-40% idle.
    >
    >BUT... starting from -j4 (and upwards) the compile time suddenly goes to
    >3.5 minutes!

    Nothing to do with the disks, it is a design flaw in the kernel build
    system. If you want a useful parallel make using -j<n>, set <n> to 3,
    4 or 5 higher than the real number of parallel jobs that you want. The
    exact value to add depends on which kernel tree you are building. See
    http://marc.theaimsgroup.com/?l=linux-kernel&m=115553906404695&w=2

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