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    SubjectRe: [performance problem] CONFIG_DYNAMIC_FTRACE: Increased kernel build times

    * John Kacur <jkacur@redhat.com> wrote:

    > 2009/10/23 Ingo Molnar <mingo@elte.hu> wrote:
    > >
    > > Steve,
    > >
    > > i did an 64-bit allyesconfig build test (with debug_info disabled), with
    > > and without CONFIG_DYNAMIC_FTRACE set.
    > >
    > > The build time results are:
    > >
    > >  -CONFIG_DYNAMIC_FTRACE:   266.30
    > >  +CONFIG_DYNAMIC_FTRACE:   296.07 (+11.2%)
    > >
    > > So we get more than 10% build time overhead.
    > >
    > > That's quite high - higher than what i remember having measured
    > > originally when the first iteration of the mcount code went in.
    > >
    > > This extra overhead comes from the mcount post-processing script
    > > (scripts/recordmcount.pl) that runs objcopy as well and is written in
    > > Perl. I think this whole angle needs to be improved - 10% is way too
    > > high of a price to pay.
    >
    > Hi Ingo, do you still have the profiling data to share with us? [...]

    no finegrained info - i did a perf stat run.

    > [...] Was the problem more in objcopy / objdump, rather than in the
    > perl script itself?

    in top i saw perl pop up most of the time, that's where i'd suspect a
    good portion of the overhead.

    Ingo
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