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

[Babu Moger]

Hi Reinette,

On 9/16/26 00:34, Reinette Chatre wrote:
> 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)

I think we can do it by checking the
rdtgrp == resctrl_kcfg.active.k_rdtgrp

> > + * @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.

ok. We can check rdtgrp == resctrl_kcfg.active.k_rdtgrp

Thanks
Babu