linux-kernel - Re: [PATCH v16 17/34] fs/resctrl: Add the functionality to assign MBM events

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Message-ID: <0b906083-8579-48e3-9f73-4d80c327a30b@intel.com>
Date: Wed, 30 Jul 2025 12:52:16 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tony.luck@...el.com>,
	<james.morse@....com>, <tglx@...utronix.de>, <mingo@...hat.com>,
	<bp@...en8.de>, <dave.hansen@...ux.intel.com>
CC: <Dave.Martin@....com>, <x86@...nel.org>, <hpa@...or.com>,
	<akpm@...ux-foundation.org>, <paulmck@...nel.org>, <rostedt@...dmis.org>,
	<Neeraj.Upadhyay@....com>, <david@...hat.com>, <arnd@...db.de>,
	<fvdl@...gle.com>, <seanjc@...gle.com>, <jpoimboe@...nel.org>,
	<pawan.kumar.gupta@...ux.intel.com>, <xin@...or.com>,
	<manali.shukla@....com>, <tao1.su@...ux.intel.com>, <sohil.mehta@...el.com>,
	<kai.huang@...el.com>, <xiaoyao.li@...el.com>, <peterz@...radead.org>,
	<xin3.li@...el.com>, <kan.liang@...ux.intel.com>,
	<mario.limonciello@....com>, <thomas.lendacky@....com>, <perry.yuan@....com>,
	<gautham.shenoy@....com>, <chang.seok.bae@...el.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<peternewman@...gle.com>, <eranian@...gle.com>
Subject: Re: [PATCH v16 17/34] fs/resctrl: Add the functionality to assign MBM
 events

Hi Babu,

On 7/25/25 11:29 AM, Babu Moger wrote:
> When supported, "mbm_event" counter assignment mode offers "num_mbm_cntrs"
> number of counters that can be assigned to RMID, event pairs and monitor
> bandwidth usage as long as it is assigned.
> 
> Add the functionality to allocate and assign a counter to an RMID, event
> pair in the domain.
> 
> If all the counters are in use, kernel will log the error message

I think dropping "kernel will" will help the text to be imperative.

> "Failed to allocate counter for <event> in domain <id>" in
> /sys/fs/resctrl/info/last_cmd_status when a new assignment is requested.

"when a new assignment is requested" can be dropped. Or alternatively:
	Log the error message "Failed to allocate counter for <event> in domain
	<id>" in /sys/fs/resctrl/info/last_cmd_status if all the counters
	are in use.

> Exit on the first failure when assigning counters across all the domains.
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---

...

> ---
>  fs/resctrl/internal.h |   3 +
>  fs/resctrl/monitor.c  | 130 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 133 insertions(+)
> 
> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
> index db3a0f12ad77..419423bdabdc 100644
> --- a/fs/resctrl/internal.h
> +++ b/fs/resctrl/internal.h
> @@ -387,6 +387,9 @@ bool closid_allocated(unsigned int closid);
>  
>  int resctrl_find_cleanest_closid(void);
>  
> +int rdtgroup_assign_cntr_event(struct rdt_mon_domain *d, struct rdtgroup *rdtgrp,
> +			       struct mon_evt *mevt);
> +

This internal.h change does not look necessary? Looking ahead this is because 
rdtgroup.c:rdtgroup_assign_cntrs() needs it, but rdtgroup_assign_cntrs()
also belongs in monitor.c, no? 

>  #ifdef CONFIG_RESCTRL_FS_PSEUDO_LOCK
>  int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp);
>  

...

> +/*
> + * rdtgroup_alloc_assign_cntr() - Allocate a counter ID and assign it to the event
> + * pointed to by @mevt and the resctrl group @rdtgrp within the domain @d.
> + *
> + * Return:
> + * 0 on success, < 0 on failure.
> + */
> +static int rdtgroup_alloc_assign_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
> +				      struct rdtgroup *rdtgrp, struct mon_evt *mevt)
> +{
> +	int cntr_id;
> +
> +	/* No action required if the counter is assigned already. */
> +	cntr_id = mbm_cntr_get(r, d, rdtgrp, mevt->evtid);
> +	if (cntr_id >= 0)
> +		return 0;
> +
> +	cntr_id = mbm_cntr_alloc(r, d, rdtgrp, mevt->evtid);
> +	if (cntr_id <  0) {

Extra space above.

> +		rdt_last_cmd_printf("Failed to allocate counter for %s in domain %d\n",
> +				    mevt->name, d->hdr.id);
> +		return cntr_id;
> +	}
> +
> +	rdtgroup_assign_cntr(r, d, mevt->evtid, rdtgrp->mon.rmid, rdtgrp->closid, cntr_id, true);
> +
> +	return 0;
> +}
> +

Reinette