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SubjectRe: [PATCH] rudimentary tracing for Classic RCU
On Thu, Oct 09, 2008 at 04:14:26PM +0900, KOSAKI Motohiro wrote:
> Hi Lai-san,
>
> > >> In this case, why not define it as:
> > >> static char buf[20*NR_CPUS + 100];
> > >
> > > Actually you should near never use NR_CPUS now but always num_possible_cpus()
> > > (or even num_online_cpus()) Using NR_CPUS can lead to extreme waste
> > > of memory on kernels which are compiled for 4096 CPUs for example.
> > >
> > > And with num_possible_cpus() kmalloc is needed.
> >
> > I thought the default value of NR_CPUS is 32.
>
> it's pointless.
> Almost distribution use _very_ large NR_CPUS (likes 4096).

Right now it's more like 8-128, but at least there is some effort
to make a 4096 CPU distribution possible and Mike Travis has been
tirelessly working on eradicating all the rogue NR_CPUs all over
the tree. So it's better to not add more.

> So, We should concern large NR_CPUS.

Agreed.

-Andi

--
ak@linux.intel.com


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