linux-kernel - Re: [PATCH v13 14/27] x86/resctrl: Add the functionality to unassign MBM events

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Message-ID: <d54c8b00-c30d-4c01-b748-34c1d87743d4@intel.com>
Date: Thu, 22 May 2025 15:49:11 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tony.luck@...el.com>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>
CC: <james.morse@....com>, <dave.martin@....com>, <fenghuay@...dia.com>,
	<x86@...nel.org>, <hpa@...or.com>, <paulmck@...nel.org>,
	<akpm@...ux-foundation.org>, <thuth@...hat.com>, <rostedt@...dmis.org>,
	<ardb@...nel.org>, <gregkh@...uxfoundation.org>,
	<daniel.sneddon@...ux.intel.com>, <jpoimboe@...nel.org>,
	<alexandre.chartre@...cle.com>, <pawan.kumar.gupta@...ux.intel.com>,
	<thomas.lendacky@....com>, <perry.yuan@....com>, <seanjc@...gle.com>,
	<kai.huang@...el.com>, <xiaoyao.li@...el.com>, <kan.liang@...ux.intel.com>,
	<xin3.li@...el.com>, <ebiggers@...gle.com>, <xin@...or.com>,
	<sohil.mehta@...el.com>, <andrew.cooper3@...rix.com>,
	<mario.limonciello@....com>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <peternewman@...gle.com>,
	<maciej.wieczor-retman@...el.com>, <eranian@...gle.com>,
	<Xiaojian.Du@....com>, <gautham.shenoy@....com>
Subject: Re: [PATCH v13 14/27] x86/resctrl: Add the functionality to unassign
 MBM events

Hi Babu,

On 5/15/25 3:51 PM, Babu Moger wrote:
> The mbm_cntr_assign mode offers "num_mbm_cntrs" number of counters that
> can be assigned to an RMID, event pair and monitor the bandwidth as long
> as it is assigned. If all the counters are in use, the kernel will log the
> error message "Unable to allocate counter in domain" in
> /sys/fs/resctrl/info/last_cmd_status when a new assignment is requested.
> 
> To make space for a new assignment, users must unassign an already
> assigned counter and retry the assignment again.
> 
> Add the functionality to unassign and free the counters in the domain.
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
...

> ---
>  fs/resctrl/internal.h |  2 ++
>  fs/resctrl/monitor.c  | 60 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 62 insertions(+)
> 
> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
> index ce4fcac91937..64ddc107fcab 100644
> --- a/fs/resctrl/internal.h
> +++ b/fs/resctrl/internal.h
> @@ -379,6 +379,8 @@ int resctrl_find_cleanest_closid(void);
>  
>  int resctrl_assign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
>  			      struct rdtgroup *rdtgrp, enum resctrl_event_id evtid);
> +int resctrl_unassign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
> +				struct rdtgroup *rdtgrp, enum resctrl_event_id evtid);
>  
>  #ifdef CONFIG_RESCTRL_FS_PSEUDO_LOCK
>  int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp);
> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
> index d76fd0840946..fbc938bd3b23 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -989,6 +989,14 @@ static int mbm_cntr_alloc(struct rdt_resource *r, struct rdt_mon_domain *d,
>  	return -ENOSPC;
>  }
>  
> +/*
> + * mbm_cntr_free() -  Reset cntr_id to zero.

"Reset cntr_id to zero"? cntr_id is an index to an array.
Please provide accurate and useful descriptions.

> + */
> +static void mbm_cntr_free(struct rdt_mon_domain *d, int cntr_id)
> +{
> +	memset(&d->cntr_cfg[cntr_id], 0, sizeof(struct mbm_cntr_cfg));
> +}
> +
>  /*
>   * mbm_get_mon_event() - Return the mon_evt entry for the matching evtid.
>   */
> @@ -1068,3 +1076,55 @@ int resctrl_assign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
>  
>  	return ret;
>  }
> +
> +/*
> + * Unassign and free the counter if assigned.
> + */
> +static int resctrl_free_config_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
> +				    struct rdtgroup *rdtgrp, enum resctrl_event_id evtid)
> +{
> +	struct mon_evt *mevt;
> +	int cntr_id;
> +
> +	cntr_id = mbm_cntr_get(r, d, rdtgrp, evtid);
> +
> +	/* If there is no cntr_id assigned, nothing to do */
> +	if (cntr_id < 0)
> +		return 0;
> +
> +	mevt = mbm_get_mon_event(r, evtid);
> +	if (!mevt) {
> +		rdt_last_cmd_printf("Invalid event id %d\n", evtid);

Similar to previous comment this is in kernel bug territory and could be simplified
by passing mon_evt instead. Although this is the unassign portion where 
evt_cfg seems unnecessary.

> +		return -EINVAL;
> +	}
> +
> +	resctrl_config_cntr(r, d, evtid, rdtgrp->mon.rmid, rdtgrp->closid,
> +			    cntr_id, mevt->evt_cfg, false);
> +
> +	mbm_cntr_free(d, cntr_id);
> +
> +	return 0;
> +}
> +
> +/*
> + * Unassign a hardware counter associated with @evtid from the domain and
> + * the group. Unassign the counters from all the domains if @d is NULL else
> + * unassign from @d.
> + */
> +int  resctrl_unassign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
> +				 struct rdtgroup *rdtgrp, enum resctrl_event_id evtid)
> +{
> +	int ret;
> +
> +	if (!d) {
> +		list_for_each_entry(d, &r->mon_domains, hdr.list) {
> +			ret = resctrl_free_config_cntr(r, d, rdtgrp, evtid);
> +			if (ret)
> +				return ret;
> +		}
> +	} else {
> +		ret = resctrl_free_config_cntr(r, d, rdtgrp, evtid);
> +	}
> +
> +	return ret;
> +}

Reinette