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Subject: Re: [Patch v4 1/3] lib: Restrict cpumask_local_spread to houskeeping
 CPUs
From:   Nitesh Narayan Lal <nitesh@redhat.com>
To:     linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        peterz@infradead.org
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Date:   Mon, 29 Jun 2020 12:11:25 -0400
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On 6/25/20 6:34 PM, Nitesh Narayan Lal wrote:
> From: Alex Belits <abelits@marvell.com>
>
> The current implementation of cpumask_local_spread() does not respect the
> isolated CPUs, i.e., even if a CPU has been isolated for Real-Time task,
> it will return it to the caller for pinning of its IRQ threads. Having
> these unwanted IRQ threads on an isolated CPU adds up to a latency
> overhead.
>
> Restrict the CPUs that are returned for spreading IRQs only to the
> available housekeeping CPUs.
>
> Signed-off-by: Alex Belits <abelits@marvell.com>
> Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>

Hi Peter,

I just realized that Yuqi jin's patch [1] that modifies cpumask_local_sprea=
d is
lying in linux-next.
Should I do a re-post by re-basing the patches on the top of linux-next?

[1]
https://lore.kernel.org/lkml/1582768688-2314-1-git-send-email-zhangshaokun@=
hisilicon.com/

> ---
>  lib/cpumask.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/lib/cpumask.c b/lib/cpumask.c
> index fb22fb266f93..85da6ab4fbb5 100644
> --- a/lib/cpumask.c
> +++ b/lib/cpumask.c
> @@ -6,6 +6,7 @@
>  #include <linux/export.h>
>  #include <linux/memblock.h>
>  #include <linux/numa.h>
> +#include <linux/sched/isolation.h>
> =20
>  /**
>   * cpumask_next - get the next cpu in a cpumask
> @@ -205,22 +206,27 @@ void __init free_bootmem_cpumask_var(cpumask_var_t =
mask)
>   */
>  unsigned int cpumask_local_spread(unsigned int i, int node)
>  {
> -=09int cpu;
> +=09int cpu, hk_flags;
> +=09const struct cpumask *mask;
> =20
> +=09hk_flags =3D HK_FLAG_DOMAIN | HK_FLAG_MANAGED_IRQ;
> +=09mask =3D housekeeping_cpumask(hk_flags);
>  =09/* Wrap: we always want a cpu. */
> -=09i %=3D num_online_cpus();
> +=09i %=3D cpumask_weight(mask);
> =20
>  =09if (node =3D=3D NUMA_NO_NODE) {
> -=09=09for_each_cpu(cpu, cpu_online_mask)
> +=09=09for_each_cpu(cpu, mask) {
>  =09=09=09if (i-- =3D=3D 0)
>  =09=09=09=09return cpu;
> +=09=09}
>  =09} else {
>  =09=09/* NUMA first. */
> -=09=09for_each_cpu_and(cpu, cpumask_of_node(node), cpu_online_mask)
> +=09=09for_each_cpu_and(cpu, cpumask_of_node(node), mask) {
>  =09=09=09if (i-- =3D=3D 0)
>  =09=09=09=09return cpu;
> +=09=09}
> =20
> -=09=09for_each_cpu(cpu, cpu_online_mask) {
> +=09=09for_each_cpu(cpu, mask) {
>  =09=09=09/* Skip NUMA nodes, done above. */
>  =09=09=09if (cpumask_test_cpu(cpu, cpumask_of_node(node)))
>  =09=09=09=09continue;
--=20
Nitesh


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