Messages in this thread | | | Date | Mon, 14 Nov 2022 16:32:09 +0200 | From | Andy Shevchenko <> | Subject | Re: [PATCH v2 3/4] sched: add sched_numa_find_nth_cpu() |
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On Sat, Nov 12, 2022 at 11:09:45AM -0800, Yury Norov wrote: > The function finds Nth set CPU in a given cpumask starting from a given > node. > > Leveraging the fact that each hop in sched_domains_numa_masks includes the > same or greater number of CPUs than the previous one, we can use binary > search on hops instead of linear walk, which makes the overall complexity > of O(log n) in terms of number of cpumask_weight() calls.
...
> +struct __cmp_key { > + const struct cpumask *cpus; > + struct cpumask ***masks; > + int node; > + int cpu; > + int w; > +}; > + > +static int cmp(const void *a, const void *b)
Calling them key and pivot (as in the caller), would make more sense.
> +{
What about
const (?) struct cpumask ***masks = (...)pivot;
> + struct cpumask **prev_hop = *((struct cpumask ***)b - 1);
= masks[-1];
> + struct cpumask **cur_hop = *(struct cpumask ***)b;
= masks[0];
?
> + struct __cmp_key *k = (struct __cmp_key *)a;
> + if (cpumask_weight_and(k->cpus, cur_hop[k->node]) <= k->cpu) > + return 1;
> + k->w = (b == k->masks) ? 0 : cpumask_weight_and(k->cpus, prev_hop[k->node]); > + if (k->w <= k->cpu) > + return 0;
Can k->cpu be negative? If no, we can rewrite above as
k->w = 0; if (b == k->masks) return 0;
k->w = cpumask_weight_and(k->cpus, prev_hop[k->node]);
> + return -1; > +}
...
> +int sched_numa_find_nth_cpu(const struct cpumask *cpus, int cpu, int node) > +{ > + struct __cmp_key k = { cpus, NULL, node, cpu, 0 };
You can drop NULL and 0 while using C99 assignments.
> + int hop, ret = nr_cpu_ids;
> + rcu_read_lock();
+ Blank line?
> + k.masks = rcu_dereference(sched_domains_numa_masks); > + if (!k.masks) > + goto unlock;
> + hop = (struct cpumask ***) > + bsearch(&k, k.masks, sched_domains_numa_levels, sizeof(k.masks[0]), cmp) - k.masks;
Strange indentation. I would rather see the split on parameters and maybe '-' operator.
sizeof(*k.masks) is a bit shorter, right?
Also we may go with
struct cpumask ***masks; struct __cmp_key k = { .cpus = cpus, .node = node, .cpu = cpu };
> + ret = hop ? > + cpumask_nth_and_andnot(cpu - k.w, cpus, k.masks[hop][node], k.masks[hop-1][node]) : > + cpumask_nth_and(cpu - k.w, cpus, k.masks[0][node]);
> +unlock:
out_unlock: shows the intention more clearly, no?
> + rcu_read_unlock(); > + return ret; > +}
-- With Best Regards, Andy Shevchenko
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