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    SubjectRe: [RFC 2/2] Make x86 calibrate_delay run in parallel.

    * Yinghai Lu <yinghai@kernel.org> wrote:

    > On Tue, Dec 14, 2010 at 5:58 PM, <Robin@sgi.com> wrote:
    > >
    > > On a 4096 cpu machine, we noticed that 318 seconds were taken for bringing
    > > up the cpus.  By specifying lpj=<value>, we reduced that to 75 seconds.
    > > Andi Kleen suggested we rework the calibrate_delay calls to run in
    > > parallel.  With that code in place, a test boot of the same machine took
    > > 61 seconds to bring the cups up.  I am not sure how we beat the lpj=
    > > case, but it did outperform.
    > >
    > > One thing to note is the total BogoMIPS value is also consistently higher.
    > > I am wondering if this is an effect with the cores being in performance
    > > mode.  I did notice that the parallel calibrate_delay calls did cause the
    > > fans on the machine to ramp up to full speed where the normal sequential
    > > calls did not cause them to budge at all.
    >
    > please check attached patch, that could calibrate correctly.
    >
    > Thanks
    >
    > Yinghai

    > [PATCH -v2] x86: Make calibrate_delay run in parallel.
    >
    > On a 4096 cpu machine, we noticed that 318 seconds were taken for bringing
    > up the cpus. By specifying lpj=<value>, we reduced that to 75 seconds.
    > Andi Kleen suggested we rework the calibrate_delay calls to run in
    > parallel.

    The risk wit tat suggestion is that it will spectacularly miscalibrate on
    hyperthreading systems.

    Thanks,

    Ingo
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