Re: [PATCH v2 1/5] smp: don't declare nr_cpu_ids if NR_CPUS == 1

[Peter Zijlstra]

On Tue, Sep 06, 2022 at 07:06:31AM -0700, Yury Norov wrote:
> On Tue, Sep 06, 2022 at 10:53:53AM +0200, Peter Zijlstra wrote:
> > On Mon, Sep 05, 2022 at 04:08:16PM -0700, Yury Norov wrote:
> > > SMP and NR_CPUS are independent options, hence nr_cpu_ids may be
> > > declared even if NR_CPUS == 1, which is useless.
> > 
> > I'm thikning you're fixing the wrong problem here.
> 
> I'm removing dead code. If NR_CPUS == 1, nr_cpu_ids does exist, exported
> as an interface variable, but never normally reached, because in some
> other piece of code (not even in smp.h) it's declared conditionally. 

Can't you simply disallow NR_CPUS==1 for SMP builds? It doesn't make
sense anyway.

> > Why do we need extra source complexity for this?
> 
> To have effective code generation for UP builds.

Again, who cares... isn't it hard to find actual UP chips these days?

It was suggested the other day we remove a whole bunch of SMP=n code and
unconditionally use SMP code, even if its pointless on UP just to make
the source simpler.