[PATCH 05/33] sched/isolation: Save boot defined domain flags

[Valentin Schneider]

On 13/10/25 22:31, Frederic Weisbecker wrote:
> HK_TYPE_DOMAIN will soon integrate not only boot defined isolcpus= CPUs
> but also cpuset isolated partitions.
>
> Housekeeping still needs a way to record what was initially passed
> to isolcpus= in order to keep these CPUs isolated after a cpuset
> isolated partition is modified or destroyed while containing some of
> them.
>
> Create a new HK_TYPE_DOMAIN_BOOT to keep track of those.
>
> Signed-off-by: Frederic Weisbecker <frederic at kernel.org>
> Reviewed-by: Phil Auld <pauld at redhat.com>
> ---
>  include/linux/sched/isolation.h | 1 +
>  kernel/sched/isolation.c        | 5 +++--
>  2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
> index d8501f4709b5..da22b038942a 100644
> --- a/include/linux/sched/isolation.h
> +++ b/include/linux/sched/isolation.h
> @@ -7,6 +7,7 @@
>  #include <linux/tick.h>
>
>  enum hk_type {
> +	HK_TYPE_DOMAIN_BOOT,
>       HK_TYPE_DOMAIN,
>       HK_TYPE_MANAGED_IRQ,
>       HK_TYPE_KERNEL_NOISE,
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index a4cf17b1fab0..8690fb705089 100644
> --- a/kernel/sched/isolation.c
> +++ b/kernel/sched/isolation.c
> @@ -11,6 +11,7 @@
>  #include "sched.h"
>
>  enum hk_flags {
> +	HK_FLAG_DOMAIN_BOOT	= BIT(HK_TYPE_DOMAIN_BOOT),
>       HK_FLAG_DOMAIN		= BIT(HK_TYPE_DOMAIN),
>       HK_FLAG_MANAGED_IRQ	= BIT(HK_TYPE_MANAGED_IRQ),
>       HK_FLAG_KERNEL_NOISE	= BIT(HK_TYPE_KERNEL_NOISE),
> @@ -216,7 +217,7 @@ static int __init housekeeping_isolcpus_setup(char *str)
>
>               if (!strncmp(str, "domain,", 7)) {
>                       str += 7;
> -			flags |= HK_FLAG_DOMAIN;
> +			flags |= HK_FLAG_DOMAIN | HK_FLAG_DOMAIN_BOOT;
>                       continue;
>               }
>
> @@ -246,7 +247,7 @@ static int __init housekeeping_isolcpus_setup(char *str)
>
>       /* Default behaviour for isolcpus without flags */
>       if (!flags)
> -		flags |= HK_FLAG_DOMAIN;
> +		flags |= HK_FLAG_DOMAIN | HK_FLAG_DOMAIN_BOOT;

I got stupidly confused by the cpumask_andnot() used later on since these
are housekeeping cpumasks and not isolated ones; AFAICT HK_FLAG_DOMAIN_BOOT
is meant to be a superset of HK_FLAG_DOMAIN - or, put in a way my brain
comprehends, NOT(HK_FLAG_DOMAIN) (i.e. runtime isolated cpumask) is a
superset of NOT(HK_FLAG_DOMAIN_BOOT) (i.e. boottime isolated cpumask),
thus the final shape of cpu_is_isolated() makes sense:

  static inline bool cpu_is_isolated(int cpu)
  {
          return !housekeeping_test_cpu(cpu, HK_TYPE_DOMAIN);
  }

Could we document that to make it a bit more explicit? Maybe something like

  enum hk_type {
        /* Set at boot-time via the isolcpus= cmdline argument */
        HK_TYPE_DOMAIN_BOOT,
        /*
         * Updated at runtime via isolated cpusets; strict subset of
         * HK_TYPE_DOMAIN_BOOT as it accounts for boot-time isolated CPUs.
         */
        HK_TYPE_DOMAIN,
        ...
  }