Re: [PATCH v2 4/5] x86/topo: Fix SNC topology mess

[Peter Zijlstra]

On Tue, Mar 03, 2026 at 12:59:46PM +0100, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> > +static u32 slit_cluster_package(int N)
> > +{
> > +	int u = topology_num_nodes_per_package();
> > +	u32 pkg_id = ~0;
> > +
> > +	for (int n = 0; n < u; n++) {
> > +		const struct cpumask *cpus = cpumask_of_node(N + n);
> > +		int cpu;
> > +
> > +		for_each_cpu(cpu, cpus) {
> > +			u32 id = topology_logical_package_id(cpu);
> > +			if (pkg_id == ~0)
> > +				pkg_id = id;
> 
> Nit: newline after the 'id' local variable definition.
> 
> > +	/*
> > +	 * Off-trace cluster.
> > +	 *
> > +	 * Notably average out the symmetric pair of off-trace clusters to
> > +	 * ensure the resulting SLIT table is symmetric.
> > +	 */
> > +	x = i - (i % u);
> > +	y = j - (j % u);
> 
> AFAICS that's an open-coded rounddown() from <linux/math.h>:
> 
> 	x = rounddown(i, u);
> 	y = rounddown(j, u);
> 
> right?

Yeah, but I can never remember those 'helpers'. That is, if I have to
spend time looking for them, they're a net negative to me.

Same reason I'm most likely to write: (x + d - 1) / d, rather than,
uhmmm, /me goes find..  DIV_ROUND_UP(). And while I did actually use
that in this series, that's only because it was already in use at the
exact spot I made a change, so I didn't have to go looking.

So sure, I can do the rounddown() thing, but really, its longer than the
thing they replace and less clear, so where's the win?