Re: [PATCH v6 7/9] lib/group_cpus: honor housekeeping config when grouping CPUs

Ming Lei
2025-05-09T02:22:31Z

On Thu, Apr 24, 2025 at 08:19:46PM +0200, Daniel Wagner wrote:
> group_cpus_evenly distributes all present CPUs into groups. This ignores
> the isolcpus configuration and assigns isolated CPUs into the groups.
>
> Make group_cpus_evenly aware of isolcpus configuration and use the
> housekeeping CPU mask as base for distributing the available CPUs into
> groups.
>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Hannes Reinecke <hare@suse.de>
> Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
> Signed-off-by: Daniel Wagner <wagi@kernel.org>
> ---
> lib/group_cpus.c | 82 +++++++++++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 79 insertions(+), 3 deletions(-)
>
> diff --git a/lib/group_cpus.c b/lib/group_cpus.c
> index 016c6578a07616959470b47121459a16a1bc99e5..707997bca55344b18f63ccfa539ba77a89d8acb6 100644
> --- a/lib/group_cpus.c
> +++ b/lib/group_cpus.c
> @@ -8,6 +8,7 @@
> #include <linux/cpu.h>
> #include <linux/sort.h>
> #include <linux/group_cpus.h>
> +#include <linux/sched/isolation.h>
>
> #ifdef CONFIG_SMP
>
> @@ -330,7 +331,7 @@ static int __group_cpus_evenly(unsigned int startgrp, unsigned int numgrps,
> }
>
> /**
> - * group_cpus_evenly - Group all CPUs evenly per NUMA/CPU locality
> + * group_possible_cpus_evenly - Group all CPUs evenly per NUMA/CPU locality
> * @numgrps: number of groups
> * @nummasks: number of initialized cpumasks
> *
> @@ -346,8 +347,8 @@ static int __group_cpus_evenly(unsigned int startgrp, unsigned int numgrps,
> * We guarantee in the resulted grouping that all CPUs are covered, and
> * no same CPU is assigned to multiple groups
> */
> -struct cpumask *group_cpus_evenly(unsigned int numgrps,
> - unsigned int *nummasks)
> +static struct cpumask *group_possible_cpus_evenly(unsigned int numgrps,
> + unsigned int *nummasks)
> {
> unsigned int curgrp = 0, nr_present = 0, nr_others = 0;
> cpumask_var_t *node_to_cpumask;
> @@ -427,6 +428,81 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps,
> *nummasks = nr_present + nr_others;
> return masks;
> }
> +
> +/**
> + * group_mask_cpus_evenly - Group all CPUs evenly per NUMA/CPU locality
> + * @numgrps: number of groups
> + * @cpu_mask: CPU to consider for the grouping
> + * @nummasks: number of initialized cpusmasks
> + *
> + * Return: cpumask array if successful, NULL otherwise. And each element
> + * includes CPUs assigned to this group.
> + *
> + * Try to put close CPUs from viewpoint of CPU and NUMA locality into
> + * same group. Allocate present CPUs on these groups evenly.
> + */
> +static struct cpumask *group_mask_cpus_evenly(unsigned int numgrps,
> + const struct cpumask *cpu_mask,
> + unsigned int *nummasks)
> +{
> + cpumask_var_t *node_to_cpumask;
> + cpumask_var_t nmsk;
> + int ret = -ENOMEM;
> + struct cpumask *masks = NULL;
> +
> + if (!zalloc_cpumask_var(&nmsk, GFP_KERNEL))
> + return NULL;
> +
> + node_to_cpumask = alloc_node_to_cpumask();
> + if (!node_to_cpumask)
> + goto fail_nmsk;
> +
> + masks = kcalloc(numgrps, sizeof(*masks), GFP_KERNEL);
> + if (!masks)
> + goto fail_node_to_cpumask;
> +
> + build_node_to_cpumask(node_to_cpumask);
> +
> + ret = __group_cpus_evenly(0, numgrps, node_to_cpumask, cpu_mask, nmsk,
> + masks);
> +
> +fail_node_to_cpumask:
> + free_node_to_cpumask(node_to_cpumask);
> +
> +fail_nmsk:
> + free_cpumask_var(nmsk);
> + if (ret < 0) {
> + kfree(masks);
> + return NULL;
> + }
> + *nummasks = ret;
> + return masks;
> +}
> +
> +/**
> + * group_cpus_evenly - Group all CPUs evenly per NUMA/CPU locality
> + * @numgrps: number of groups
> + * @nummasks: number of initialized cpusmasks
> + *
> + * Return: cpumask array if successful, NULL otherwise.
> + *
> + * group_possible_cpus_evently() is used for distributing the cpus on all

s/evently/evenly/

> + * possible cpus in absence of isolcpus command line argument.

s/isolcpus/isolcpus=io_queue

> + * group_mask_cpu_evenly() is used when the isolcpus command line
> + * argument is used with managed_irq option. In this case only the

s/managed_irq/io_queue

> + * housekeeping CPUs are considered.

I'd suggest to highlight the difference, which is one fundamental thing,
originally all CPUs are covered, now only housekeeping CPUs are
distributed.

Otherwise, looks fine to me:

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Thanks,
Ming