Re: [PATCH v6 11/18] fs/resctrl: Introduce kmode_cpus/kmode_cpus_list per rdtgroup

[Moger, Babu]

Hi Reinette,


On 10/15/2026 10:31 AM, Reinette Chatre wrote:
> Hi Babu,
>
> On 10/1/26 8:10 AM, Babu Moger wrote:
> > The RESCTRL_GLOBAL_ENABLE_PER_CPU kernel mode allows tasks to use different
> > allocation and monitoring associations when transitioning from user mode to
>
> Could "different allocation and monitoring associations" just be "different
> CLOSID and RMID" (in places where this is what it refers to)? Being specific
> and consistent with terms would make this so much easier to understand.

I avoided using CLOSID and RMID terms in filesystem specific code. If 
you are ok with that then I will use these terms.

> > kernel mode. The mode is enabled/disabled on a per-CPU basis.
> >
> > Add kmode_cpus and kmode_cpus_list to display the CPUs associated with a
> > kernel mode. These files are exposed only when the global_enable_per_cpu
>
>
> "a kernel mode" -> this is specific to RESCTRL_GLOBAL_ENABLE_PER_CPU kernel
> mode node?

Sure.

> This switches from "RESCTRL_GLOBAL_ENABLE_PER_CPU kernel mode" to
> "global_enable_per_cpu mode" mid changelog.

Will change it.

> > mode is active.
> >
> > Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
> > ---
>
> ...> ---
> >   fs/resctrl/internal.h |  2 ++
> >   fs/resctrl/rdtgroup.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> >   2 files changed, 44 insertions(+)
> >
> > diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
> > index 986b9c942fb2..6b8d14c4bd83 100644
> > --- a/fs/resctrl/internal.h
> > +++ b/fs/resctrl/internal.h
> > @@ -216,6 +216,7 @@ struct mongroup {
> >    * @mon:			mongroup related data
> >    * @mode:			mode of resource group
> >    * @mba_mbps_event:		input monitoring event id when mba_sc is enabled
> > + * @kmode_cpu_mask:		CPUs in this group's kernel-mode association
>
> Could there be a caveat that the value is only valid when the resource group
> is backing the RESCTRL_GLOBAL_ENABLE_PER_CPU kernel mode?

Sure.

> >    * @plr:			pseudo-locked region
> >    */
> >   struct rdtgroup {
> > @@ -229,6 +230,7 @@ struct rdtgroup {
> >   	struct mongroup			mon;
> >   	enum rdtgrp_mode		mode;
> >   	enum resctrl_event_id		mba_mbps_event;
> > +	struct cpumask			kmode_cpu_mask;
> >   	struct pseudo_lock_region	*plr;
> >   };
> >   
> > diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
> > index 46b2cafd9411..0e638dc654c1 100644
> > --- a/fs/resctrl/rdtgroup.c
> > +++ b/fs/resctrl/rdtgroup.c
> > @@ -385,6 +385,31 @@ static int rdtgroup_cpus_show(struct kernfs_open_file *of,
> >   	return ret;
> >   }
> >   
> > +/*
> > + * Display CPU masks for the kernel-mode associated resource group.
>
> nit: "masks for" -> "mask of"?

Sure.

> > + * 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 != resctrl_kmode.rdtgrp)
>
> Could the changelog please help reader understand the patches better?
> For example, the additional "rdtgrp != resctrl_kmode.rdtgrp" check is
> subtle but very important to maintain synchronization, but it is
> never mentioned why this is used.

Will add a line in changelog about this check.

Thanks
Babu