Re: [PATCH v3] pseries: prevent free CPU ids to be reused on another node

[Laurent Dufour]

Le 07/04/2021 à 16:55, Nathan Lynch a écrit :
> Laurent Dufour <ldufour@xxxxxxxxxxxxx> writes:
> > Changes since V2, addressing Nathan's comments:
> >   - Remove the retry feature
> >   - Reduce the number of local variables (removing 'i')
>
> I was more interested in not having two variables for NUMA nodes in the
> function named 'node' and 'nid', hoping at least one of them could have
> a more descriptive name. See below.
>
> >   static int pseries_add_processor(struct device_node *np)
> >   {
> > -	unsigned int cpu;
> > +	unsigned int cpu, node;
> >   	cpumask_var_t candidate_mask, tmp;
> > -	int err = -ENOSPC, len, nthreads, i;
> > +	int err = -ENOSPC, len, nthreads, nid;
> >   	const __be32 *intserv;
> >   
> >   	intserv = of_get_property(np, "ibm,ppc-interrupt-server#s", &len);
> > @@ -163,9 +169,17 @@ static int pseries_add_processor(struct device_node *np)
> >   	zalloc_cpumask_var(&candidate_mask, GFP_KERNEL);
> >   	zalloc_cpumask_var(&tmp, GFP_KERNEL);
> >   
> > +	/*
> > +	 * Fetch from the DT nodes read by dlpar_configure_connector() the NUMA
> > +	 * node id the added CPU belongs to.
> > +	 */
> > +	nid = of_node_to_nid(np);
> > +	if (nid < 0 || !node_possible(nid))
> > +		nid = first_online_node;
> > +
> >   	nthreads = len / sizeof(u32);
> > -	for (i = 0; i < nthreads; i++)
> > -		cpumask_set_cpu(i, tmp);
> > +	for (cpu = 0; cpu < nthreads; cpu++)
> > +		cpumask_set_cpu(cpu, tmp);
> >   
> >   	cpu_maps_update_begin();
> >   
> > @@ -173,6 +187,19 @@ static int pseries_add_processor(struct device_node *np)
> >   
> >   	/* Get a bitmap of unoccupied slots. */
> >   	cpumask_xor(candidate_mask, cpu_possible_mask, cpu_present_mask);
> > +
> > +	/*
> > +	 * Remove free ids previously assigned on the other nodes. We can walk
> > +	 * only online nodes because once a node became online it is not turned
> > +	 * offlined back.
> > +	 */
> > +	for_each_online_node(node) {
> > +		if (node == nid) /* Keep our node's recorded ids */
> > +			continue;
> > +		cpumask_andnot(candidate_mask, candidate_mask,
> > +			       node_recorded_ids_map[node]);
> > +	}
> > +
>
> e.g. change 'nid' to 'assigned_node' or similar, and I think this
> becomes easier to follow.

Fair enough, will send a v4

> Otherwise the patch looks fine to me now.