linux-kernel - Re: [PATCH v8 18/25] x86/resctrl: Add the interface to unassign a MBM counter

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Message-ID: <a74315f3-9250-4e52-823b-dfadf87a6142@intel.com>
Date: Tue, 15 Oct 2024 20:29:40 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <fenghua.yu@...el.com>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <paulmck@...nel.org>,
	<rdunlap@...radead.org>, <tj@...nel.org>, <peterz@...radead.org>,
	<yanjiewtw@...il.com>, <kim.phillips@....com>, <lukas.bulwahn@...il.com>,
	<seanjc@...gle.com>, <jmattson@...gle.com>, <leitao@...ian.org>,
	<jpoimboe@...nel.org>, <rick.p.edgecombe@...el.com>,
	<kirill.shutemov@...ux.intel.com>, <jithu.joseph@...el.com>,
	<kai.huang@...el.com>, <kan.liang@...ux.intel.com>,
	<daniel.sneddon@...ux.intel.com>, <pbonzini@...hat.com>,
	<sandipan.das@....com>, <ilpo.jarvinen@...ux.intel.com>,
	<peternewman@...gle.com>, <maciej.wieczor-retman@...el.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<eranian@...gle.com>, <james.morse@....com>
Subject: Re: [PATCH v8 18/25] x86/resctrl: Add the interface to unassign a MBM
 counter

Hi Babu,

On 10/9/24 10:39 AM, Babu Moger wrote:
> The mbm_cntr_assign mode provides a limited number of hardware counters
> that can be assigned to an RMID-event pair to monitor bandwidth while
> assigned. If all counters are in use, the kernel will show an error
> message: "Out of MBM assignable counters" when a new assignment is
> requested. To make space for a new assignment, users must unassign an
> already assigned counter.
> 
> Introduce an interface that allows for the unassignment of counter IDs
> from both the group and the domain. Additionally, ensure that the global
> counter is released if it is no longer assigned to any domains.

Needs imperative tone ... "Release the global counter ..."

> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
...

> ---
>  arch/x86/kernel/cpu/resctrl/internal.h |  2 +
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 56 ++++++++++++++++++++++++++
>  2 files changed, 58 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 900e18aea2c4..6f388d20fb22 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -717,6 +717,8 @@ int resctrl_arch_config_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
>  			     u32 cntr_id, bool assign);
>  int rdtgroup_assign_cntr_event(struct rdt_resource *r, struct rdtgroup *rdtgrp,
>  			       struct rdt_mon_domain *d, enum resctrl_event_id evtid);
> +int rdtgroup_unassign_cntr_event(struct rdt_resource *r, struct rdtgroup *rdtgrp,
> +				 struct rdt_mon_domain *d, enum resctrl_event_id evtid);
>  void rdt_staged_configs_clear(void);
>  bool closid_allocated(unsigned int closid);
>  int resctrl_find_cleanest_closid(void);
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index e4f628e6fe65..791258adcbda 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -1945,6 +1945,62 @@ int rdtgroup_assign_cntr_event(struct rdt_resource *r, struct rdtgroup *rdtgrp,
>  	return ret;
>  }
>  
> +static bool mbm_cntr_assigned_to_domain(struct rdt_resource *r, u32 cntr_id)
> +{
> +	struct rdt_mon_domain *d;
> +
> +	list_for_each_entry(d, &r->mon_domains, hdr.list)
> +		if (test_bit(cntr_id, d->mbm_cntr_map))
> +			return 1;
> +
> +	return 0;
> +}
> +
> +/*
> + * Unassign a hardware counter from the domain and the group.

Not sure ... maybe "Unassign a hardware counter associated with @evtid from
the domain and the group."?

> + * Counter will be unassigned in all the domains if rdt_mon_domain is NULL

Please use imperative tone: "Unassign the counter from all the domains ...."

> + * else the counter will be assigned to specific domain.

copy&paste error?
"assigned to specific domain" -> "unassign from specific domain"?

> + * Global counter will be freed once it is unassigned from all the domains.

Needs imperative tone.

> + */
> +int rdtgroup_unassign_cntr_event(struct rdt_resource *r, struct rdtgroup *rdtgrp,
> +				 struct rdt_mon_domain *d, enum resctrl_event_id evtid)
> +{
> +	int index = MBM_EVENT_ARRAY_INDEX(evtid);
> +	int cntr_id = rdtgrp->mon.cntr_id[index];
> +	int ret;
> +
> +	/* Return early if the counter is unassigned already */
> +	if (cntr_id == MON_CNTR_UNSET)
> +		return 0;
> +
> +	if (!d) {
> +		list_for_each_entry(d, &r->mon_domains, hdr.list) {
> +			ret = resctrl_arch_config_cntr(r, d, evtid, rdtgrp->mon.rmid,
> +						       rdtgrp->closid, cntr_id, false);
> +			if (ret)
> +				goto out_done_unassign;
> +
> +			clear_bit(cntr_id, d->mbm_cntr_map);
> +		}
> +	} else {
> +		ret = resctrl_arch_config_cntr(r, d, evtid, rdtgrp->mon.rmid,
> +					       rdtgrp->closid, cntr_id, false);
> +		if (ret)
> +			goto out_done_unassign;
> +
> +		clear_bit(cntr_id, d->mbm_cntr_map);

Please see comment to previous patch about the duplicate snippets. Snippets can be
replaced with single function that also resets architectural state.

> +	}
> +
> +	/* Update the counter bitmap */

What is the update?

> +	if (!mbm_cntr_assigned_to_domain(r, cntr_id)) {
> +		mbm_cntr_free(r, cntr_id);
> +		rdtgrp->mon.cntr_id[index] = MON_CNTR_UNSET;
> +	}
> +
> +out_done_unassign:
> +	return ret;
> +}
> +
>  /* rdtgroup information files for one cache resource. */
>  static struct rftype res_common_files[] = {
>  	{


Reinette