Re: [PATCH v5 11/16] fs/resctrl: Introduce kmode_cpus/kmode_cpus_list per rdtgroup

[Reinette Chatre <reinette.chatre@intel.com>]

Hi Babu,

On 8/26/26 12:32 PM, Babu Moger wrote:
>  fs/resctrl/internal.h |  5 +++++
>  fs/resctrl/rdtgroup.c | 43 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 48 insertions(+)
> 
> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
> index b56f95625072..01f9f596f9b1 100644
> --- a/fs/resctrl/internal.h
> +++ b/fs/resctrl/internal.h
> @@ -216,6 +216,9 @@ struct mongroup {
>   * @mon:			mongroup related data
>   * @mode:			mode of resource group
>   * @mba_mbps_event:		input monitoring event id when mba_sc is enabled
> + * @kmode:			true if this group has an active kernel-mode
> + *				association

This really just seems specific to the global per-CPU kernel mode. Why is
it necessary? Is resctrl_kcfg.active.k_rdtgrp not sufficient by itself? (more below)

> + * @kmode_cpu_mask:		CPUs in this group's kernel-mode association
>   * @plr:			pseudo-locked region
>   */
>  struct rdtgroup {
> @@ -229,6 +232,8 @@ struct rdtgroup {
>  	struct mongroup			mon;
>  	enum rdtgrp_mode		mode;
>  	enum resctrl_event_id		mba_mbps_event;
> +	bool				kmode;
> +	struct cpumask			kmode_cpu_mask;
>  	struct pseudo_lock_region	*plr;
>  };
>  
> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
> index d2fff8adf915..06e74b027044 100644
> --- a/fs/resctrl/rdtgroup.c
> +++ b/fs/resctrl/rdtgroup.c
> @@ -389,6 +389,32 @@ static int rdtgroup_cpus_show(struct kernfs_open_file *of,
>  	return ret;
>  }
>  
> +/*
> + * Display CPU masks for the kernel-mode associated resource group.
> + * Supports both "kmode_cpus" (bitmap format) and "kmode_cpus_list"
> + * (range list format); the output format is selected accordingly.
> + *
> + * Returns -ENOENT on error.
> + */
> +static int rdtgroup_kmode_cpus_show(struct kernfs_open_file *of,
> +				    struct seq_file *s, void *v)
> +{
> +	struct rdtgroup *rdtgrp;
> +	int ret = 0;
> +
> +	rdtgrp = rdtgroup_kn_lock_live(of->kn);
> +
> +	if (rdtgrp && rdtgrp->kmode) {

First, it would be helpful to explain why the second test is needed since it
is not obvious that a resource group may get re-assigned while a user has this
file open.

Second, could a check of rdtgrp->kmode be replaced with a comparison between
rdtgrp and resctrl_kcfg.active.k_rdtgrp ? If so, why is rdtgrp::kmode needed?
I think one part of this is how this series blurs between a generic
"kernel mode" and the specific only-supported global per-CPU kernel mode
that makes it difficult to know what state can be used.

> +		seq_printf(s, is_cpu_list(of) ? "%*pbl\n" : "%*pb\n",
> +			   cpumask_pr_args(&rdtgrp->kmode_cpu_mask));
> +	} else {
> +		ret = -ENOENT;
> +	}
> +	rdtgroup_kn_unlock(of->kn);
> +
> +	return ret;
> +}
> +
>  /*
>   * Update the PGR_ASSOC MSR on all cpus in @cpu_mask,
>   *
> @@ -2288,6 +2314,23 @@ static struct rftype res_common_files[] = {
>  		.flags		= RFTYPE_FLAGS_CPUS_LIST,
>  		.fflags		= RFTYPE_BASE,
>  	},
> +	{
> +		.name		= "kmode_cpus",
> +		.mode		= 0444,
> +		.hidden		= true,
> +		.kf_ops		= &rdtgroup_kf_single_ops,
> +		.seq_show	= rdtgroup_kmode_cpus_show,
> +		.fflags		= RFTYPE_BASE,
> +	},
> +	{
> +		.name		= "kmode_cpus_list",
> +		.mode		= 0444,
> +		.hidden		= true,
> +		.kf_ops		= &rdtgroup_kf_single_ops,
> +		.seq_show	= rdtgroup_kmode_cpus_show,
> +		.flags		= RFTYPE_FLAGS_CPUS_LIST,
> +		.fflags		= RFTYPE_BASE,
> +	},
>  	{
>  		.name		= "tasks",
>  		.mode		= 0644,

Reinette