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    SubjectRe: RCU NOHZ, tsc, and clock_gettime
    On Fri, Oct 12, 2012 at 02:27:01PM -0400, Prarit Bhargava wrote:
    >
    > > The effect of removing the two functions you noted (on 3.6 and earlier)
    > > is to prevent RCU from checking for dyntick-idle CPUs, likely incurring
    > > a cache miss for each CPU with interrupts disabled. If you have a lot
    > > of CPUs (or even if NR_CPUS is large and you have a smaller number of
    > > CPUs), this can result in user-space-visible delays.
    > >
    >
    > Paul,
    >
    > I built a kernel with NR_CPUS=48 and booted on a 48 cpu (logical) system. I do
    > not see a difference in the test -- the variance is AFAICT just as large as if I
    > had run with NR_CPUS=4096.

    OK -- have you applied John Stultz's suggestions?

    Thanx, Paul



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