Commit 2ac4980c authored by Yury Norov's avatar Yury Norov Committed by Jakub Kicinski
Browse files

lib/cpumask: update comment for cpumask_local_spread() 



Now that we have an iterator-based alternative for a very common case
of using cpumask_local_spread for all cpus in a row, it's worth to
mention that in comment to cpumask_local_spread().

Signed-off-by: default avatarYury Norov <yury.norov@gmail.com>
Reviewed-by: default avatarValentin Schneider <vschneid@redhat.com>
Reviewed-by: default avatarTariq Toukan <tariqt@nvidia.com>
Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 2acda577

lib/cpumask.c

+22 −4
Original line number Diff line number Diff line
@@ -114,11 +114,29 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask) 
 * @i: index number

 * @node: local numa_node

 *

 * This function selects an online CPU according to a numa aware policy;

 * local cpus are returned first, followed by non-local ones, then it

 * wraps around.

 * Returns online CPU according to a numa aware policy; local cpus are returned

 * first, followed by non-local ones, then it wraps around.

 *

 * It's not very efficient, but useful for setup.

 * For those who wants to enumerate all CPUs based on their NUMA distances,

 * i.e. call this function in a loop, like:

 *

 * for (i = 0; i < num_online_cpus(); i++) {

 *	cpu = cpumask_local_spread(i, node);

 *	do_something(cpu);

 * }

 *

 * There's a better alternative based on for_each()-like iterators:

 *

 *	for_each_numa_hop_mask(mask, node) {

 *		for_each_cpu_andnot(cpu, mask, prev)

 *			do_something(cpu);

 *		prev = mask;

 *	}

 *

 * It's simpler and more verbose than above. Complexity of iterator-based

 * enumeration is O(sched_domains_numa_levels * nr_cpu_ids), while

 * cpumask_local_spread() when called for each cpu is

 * O(sched_domains_numa_levels * nr_cpu_ids * log(nr_cpu_ids)).

 */

unsigned int cpumask_local_spread(unsigned int i, int node)

{