linux-kernel - Re: [PATCH v11 11/23] x86/resctrl: Introduce mbm_cntr_cfg to track assignable counters at domain

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Message-ID: <b88868e1-52b2-4a66-bec2-e0846394b74b@intel.com>
Date: Wed, 5 Feb 2025 15:57:14 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>,
	<tony.luck@...el.com>, <peternewman@...gle.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <paulmck@...nel.org>,
	<akpm@...ux-foundation.org>, <thuth@...hat.com>, <rostedt@...dmis.org>,
	<xiongwei.song@...driver.com>, <pawan.kumar.gupta@...ux.intel.com>,
	<daniel.sneddon@...ux.intel.com>, <jpoimboe@...nel.org>,
	<perry.yuan@....com>, <sandipan.das@....com>, <kai.huang@...el.com>,
	<xiaoyao.li@...el.com>, <seanjc@...gle.com>, <xin3.li@...el.com>,
	<andrew.cooper3@...rix.com>, <ebiggers@...gle.com>,
	<mario.limonciello@....com>, <james.morse@....com>,
	<tan.shaopeng@...itsu.com>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <maciej.wieczor-retman@...el.com>,
	<eranian@...gle.com>
Subject: Re: [PATCH v11 11/23] x86/resctrl: Introduce mbm_cntr_cfg to track
 assignable counters at domain

Hi Babu,

On 1/22/25 12:20 PM, Babu Moger wrote:
> In mbm_cntr_assign mode hardware counters are assigned/unassigned to an
> MBM event of a monitor group. Hardware counters are assigned/unassigned
> at monitoring domain level.
> 
> Manage a monitoring domain's hardware counters using a per monitoring
> domain array of struct mbm_cntr_cfg that is indexed by the hardware
> counter	ID. A hardware counter's configuration contains the MBM event

Something strange in this changelog with a few random \t in the text.

> ID and points to the monitoring group that it is assigned to, with a
> NULL pointer meaning that the hardware counter is available for assignment.
> 
> There is no direct way to determine which hardware counters are	assigned

... another \t above 

> to a particular monitoring group. Check every entry of every hardware
> counter	configuration array in every monitoring domain to query which

... one more \t above

> MBM events of a monitoring group is tracked by hardware. Such queries
> are acceptable because of a very small number of assignable counters.

It is not obvious what "very small number" means. Is it possible to give
a range to help reader understand the motivation?

> 
> Suggested-by: Peter Newman <peternewman@...gle.com>
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---

> ---
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 11 +++++++++++
>  include/linux/resctrl.h                | 14 ++++++++++++++
>  2 files changed, 25 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 18110a1afb6d..75a3b56996ca 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -4009,6 +4009,7 @@ static void __init rdtgroup_setup_default(void)
>  
>  static void domain_destroy_mon_state(struct rdt_mon_domain *d)
>  {
> +	kfree(d->cntr_cfg);
>  	bitmap_free(d->rmid_busy_llc);
>  	kfree(d->mbm_total);
>  	kfree(d->mbm_local);
> @@ -4082,6 +4083,16 @@ static int domain_setup_mon_state(struct rdt_resource *r, struct rdt_mon_domain
>  			return -ENOMEM;
>  		}
>  	}
> +	if (is_mbm_enabled() && r->mon.mbm_cntr_assignable) {
> +		tsize = sizeof(*d->cntr_cfg);
> +		d->cntr_cfg = kcalloc(r->mon.num_mbm_cntrs, tsize, GFP_KERNEL);
> +		if (!d->cntr_cfg) {
> +			bitmap_free(d->rmid_busy_llc);
> +			kfree(d->mbm_total);
> +			kfree(d->mbm_local);
> +			return -ENOMEM;
> +		}
> +	}
>  
>  	return 0;
>  }
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 511cfce8fc21..9a54e307d340 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -94,6 +94,18 @@ struct rdt_ctrl_domain {
>  	u32				*mbps_val;
>  };
>  
> +/**
> + * struct mbm_cntr_cfg - assignable counter configuration
> + * @evtid:		 MBM event to which the counter is assigned. Only valid
> + *			 if @rdtgroup is not NULL.
> + * @rdtgroup:		 resctrl group assigned to the counter. NULL if the
> + *			 counter is free.
> + */
> +struct mbm_cntr_cfg {
> +	enum resctrl_event_id	evtid;
> +	struct rdtgroup		*rdtgrp;
> +};
> +

$ scripts/kernel-doc -v -none include/linux/resctrl.h                           
...                                                                             
include/linux/resctrl.h:107: warning: Function parameter or struct member 'rdtgrp' not described in 'mbm_cntr_cfg'
include/linux/resctrl.h:107: warning: Excess struct member 'rdtgroup' description in 'mbm_cntr_cfg'
...                                            

>  /**
>   * struct rdt_mon_domain - group of CPUs sharing a resctrl monitor resource
>   * @hdr:		common header for different domain types
> @@ -105,6 +117,7 @@ struct rdt_ctrl_domain {
>   * @cqm_limbo:		worker to periodically read CQM h/w counters
>   * @mbm_work_cpu:	worker CPU for MBM h/w counters
>   * @cqm_work_cpu:	worker CPU for CQM h/w counters
> + * @cntr_cfg:		assignable counters configuration
>   */
>  struct rdt_mon_domain {
>  	struct rdt_domain_hdr		hdr;
> @@ -116,6 +129,7 @@ struct rdt_mon_domain {
>  	struct delayed_work		cqm_limbo;
>  	int				mbm_work_cpu;
>  	int				cqm_work_cpu;
> +	struct mbm_cntr_cfg		*cntr_cfg;
>  };
>  
>  /**

Reinette