Re: [PATCH v15 29/34] x86,fs/resctrl: Auto assign counters on mkdir and clean up on group removal

[Moger, Babu]

Hi Reinette,

On 7/17/2025 10:56 PM, Reinette Chatre wrote:
> Hi Babu,
>
> On 7/8/25 3:17 PM, Babu Moger wrote:
> > Resctrl provides a user-configurable option mbm_assign_on_mkdir that
> > determines if a counter will automatically be assigned to an RMID, event
> > pair when its associated monitor group is created via mkdir.
> >
> > Enable mbm_assign_on_mkdir by default and automatically assign the counters
> > when a resctrl group is created.
> >
> > Counters allocated to a resctrl group should be released when the group is
> > deleted. Add support to unassign and free counters during the group
> > teardown.
> >
> > By default, each group requires two counters: one for the MBM total event
> > and one for the MBM local event.
> >
> > If the counters are exhausted, the kernel will log the error message
> > "Unable to allocate counter in domain" in
> > /sys/fs/resctrl/info/last_cmd_status when a new group is created and the
> > counter assignment will fail. However, the creation of a group should not
> > fail due to assignment failures. Users have the flexibility to modify the
> > assignments at a later time.
>
> I find that this changelog jumps around a bit. Below is an attempt at some
> re-organization. Please feel free to improve:
>
> 	Resctrl provides a user-configurable option mbm_assign_on_mkdir that
> 	determines if a counter will automatically be assigned to an RMID, event
> 	pair when its associated monitor group is created via mkdir.
>                                                                                  
> 	Enable mbm_assign_on_mkdir by default to automatically assign
> 	counters to the two default events (MBM total and MBM local) of a new
> 	monitoring group created via mkdir. This maintains backward compatibility
> 	with original resctrl support for these two events.
>                                                                                  
> 	Unassign and free counters belonging to a monitoring group when the group is
> 	deleted.
>                                                                                  
> 	Monitor group creation does not fail if a counter cannot be assigned to
> 	one or both events. There may be limited counters and users have the
> 	flexibility to modify counter assignments at a later time.
> 	Log the error message "Unable to allocate counter in domain" in
> 	/sys/fs/resctrl/info/last_cmd_status when a new monitoring group is created
> 	but counter assignment failed.

Looks good. Thanks

> > Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
> > ---
>
> ...
>
> > ---
> >   arch/x86/kernel/cpu/resctrl/monitor.c |  1 +
> >   fs/resctrl/rdtgroup.c                 | 70 ++++++++++++++++++++++++++-
> >   2 files changed, 69 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> > index 026c2e2d19d3..e0706083fe0e 100644
> > --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> > +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> > @@ -457,6 +457,7 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
> >   		r->mon.mbm_cntr_assignable = true;
> >   		cpuid_count(0x80000020, 5, &eax, &ebx, &ecx, &edx);
> >   		r->mon.num_mbm_cntrs = (ebx & GENMASK(15, 0)) + 1;
> > +		r->mon.mbm_assign_on_mkdir = true;
>
> This is a resctrl fs default. Should it not be set in
> resctrl_mon_resource_init()?

Yes. Moved it in resctrl_mon_resource_init().

> >   	}
> >   
> >   	r->mon_capable = true;
> > diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
> > index b7289ce2b3a6..645245f274e9 100644
> > --- a/fs/resctrl/rdtgroup.c
> > +++ b/fs/resctrl/rdtgroup.c
> > @@ -2884,6 +2884,54 @@ static void schemata_list_destroy(void)
> >   	}
> >   }
> >   
> > +/*
> > + * rdtgroup_assign_cntrs() - Assign counters to MBM events. Called when
> > + *			     a new group is created.
> > + * If "mbm_event" counter assignment mode is enabled, counters should be
> > + * automatically assigned if the "mbm_assign_on_mkdir" is set.
> > + * Each group can accommodate two counters: one for the total event and
>
> "Each group can accommodate two counters" -> "Each group can accommodate two counters
> per domain"?
Sure.

> > + * one for the local event. Assignments may fail due to the limited number
> > + * of counters. However, it is not necessary to fail the group creation
> > + * and thus no failure is returned. Users have the option to modify the
> > + * counter assignments after the group has been created.
> > + */
> > +static void rdtgroup_assign_cntrs(struct rdtgroup *rdtgrp)
> > +{
> > +	struct rdt_resource *r = resctrl_arch_get_resource(RDT_RESOURCE_L3);
> > +
> > +	if (!r->mon_capable || !resctrl_arch_mbm_cntr_assign_enabled(r) ||
> > +	    !r->mon.mbm_assign_on_mkdir)
> > +		return;
> > +
> > +	if (resctrl_is_mon_event_enabled(QOS_L3_MBM_TOTAL_EVENT_ID))
> > +		rdtgroup_assign_cntr_event(NULL, rdtgrp,
> > +					   &mon_event_all[QOS_L3_MBM_TOTAL_EVENT_ID]);
> > +
> > +	if (resctrl_is_mon_event_enabled(QOS_L3_MBM_LOCAL_EVENT_ID))
> > +		rdtgroup_assign_cntr_event(NULL, rdtgrp,
> > +					   &mon_event_all[QOS_L3_MBM_LOCAL_EVENT_ID]);
> > +}
> > +
>
> Reinette

Thanks
Babu