Re: RCU NOHZ, tsc, and clock_gettime

[Prarit Bhargava]

> 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.

P.
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