Re: [PATCH v8 19/25] x86/resctrl: Auto assign/unassign counters when mbm_cntr_assign is enabled

[Moger, Babu]

Hi Tony,

On 10/11/2024 12:17 PM, Tony Luck wrote:
> On Wed, Oct 09, 2024 at 12:39:44PM -0500, Babu Moger wrote:
> > +/*
> > + * Called when a new group is created. If `mbm_cntr_assign` mode is enabled,
> > + * counters are automatically assigned. Each group requires two counters:
> > + * one for the total event and one for the local event. Due to the limited
> > + * number of counters, assignments may fail in some cases. However, it is
> > + * not necessary to fail the group creation. Users have the option to
> > + * modify the assignments after the group has been created.
> > + */
> > +static int rdtgroup_assign_cntrs(struct rdtgroup *rdtgrp)
> > +{
> > +	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
> > +	int ret = 0;
> > +
> > +	if (!resctrl_arch_mbm_cntr_assign_enabled(r))
> > +		return 0;
> > +
> > +	if (is_mbm_total_enabled())
> > +		ret = rdtgroup_assign_cntr_event(r, rdtgrp, NULL, QOS_L3_MBM_TOTAL_EVENT_ID);
> > +
> > +	if (!ret && is_mbm_local_enabled())
> > +		ret = rdtgroup_assign_cntr_event(r, rdtgrp, NULL, QOS_L3_MBM_LOCAL_EVENT_ID);
>
> This overwrites the value from allocating the counter for total event.

Total event and local events have two different indexes.
Can you please elaborate?

> > +
> > +	return ret;
>
> But none of the callers check the return. Indeed it is ok (and
> expected) that counter allocation can fail.
>
> Just make this a "void" function and delete the "ret" local variable.

Comment below.
> > +}
> > +
> > +/*
> > + * Called when a group is deleted. Counters are unassigned if it was in
> > + * assigned state.
> > + */
> > +static int rdtgroup_unassign_cntrs(struct rdtgroup *rdtgrp)
> > +{
> > +	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
> > +	int ret = 0;
> > +
> > +	if (!resctrl_arch_mbm_cntr_assign_enabled(r))
> > +		return 0;
> > +
> > +	if (is_mbm_total_enabled())
> > +		ret = rdtgroup_unassign_cntr_event(r, rdtgrp, NULL, QOS_L3_MBM_TOTAL_EVENT_ID);
> > +
> > +	if (!ret && is_mbm_local_enabled())
> > +		ret = rdtgroup_unassign_cntr_event(r, rdtgrp, NULL, QOS_L3_MBM_LOCAL_EVENT_ID);
> > +
> > +	return ret;
>
> Ditto. No caller checks. Make this a void function. Dig down the
> call chain here. It looks like rdtgroup_unassign_cntr_event() can't
> fail, so it should be a void function too. Ditto resctrl_arch_config_cntr()

It was started a void function. In this case all the call sequence 
return 0. There is a possibility that other architectures can return 
failure(in arch calls resctrl_arch_config_cntr()). Keeping that in mind 
we added the check to handle the return values. Hope that helps.
Thanks
--
- Babu Moger