linux-kernel - Re: [PATCH v14 30/32] fs/resctrl: Hide the BMEC related files when mbm

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Message-ID: <3c753f3c-e91b-4cfe-983d-efe8ff07b750@intel.com>
Date: Wed, 25 Jun 2025 16:39:19 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tony.luck@...el.com>,
	<Dave.Martin@....com>, <james.morse@....com>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <akpm@...ux-foundation.org>,
	<rostedt@...dmis.org>, <paulmck@...nel.org>, <thuth@...hat.com>,
	<ardb@...nel.org>, <gregkh@...uxfoundation.org>, <seanjc@...gle.com>,
	<thomas.lendacky@....com>, <pawan.kumar.gupta@...ux.intel.com>,
	<manali.shukla@....com>, <perry.yuan@....com>, <kai.huang@...el.com>,
	<peterz@...radead.org>, <xiaoyao.li@...el.com>, <kan.liang@...ux.intel.com>,
	<mario.limonciello@....com>, <xin3.li@...el.com>, <gautham.shenoy@....com>,
	<xin@...or.com>, <chang.seok.bae@...el.com>, <fenghuay@...dia.com>,
	<peternewman@...gle.com>, <maciej.wieczor-retman@...el.com>,
	<eranian@...gle.com>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v14 30/32] fs/resctrl: Hide the BMEC related files when
 mbm_event mode is enabled

Hi Babu,

On 6/13/25 2:05 PM, Babu Moger wrote:
> BMEC (Bandwidth Monitoring Event Configuration) and mbm_event mode do not
> work simultaneously.

Could you please elaborate why they do not work simultaneously?

> 
> When mbm_event mode is enabled, hide BMEC-related files to avoid confusion
> and update the mon_features display accordingly.
> 
> The files /sys/fs/resctrl/info/L3_MON/mbm_total_bytes_config and
> /sys/fs/resctrl/info/L3_MON/mbm_local_bytes_config will not be visible
> when mbm_event mode is enabled.
> 
> Suggested-by: Reinette Chatre <reinette.chatre@...el.com>
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
> v14: Updated the changelog for change in mbm_assign_modes.
>      Added check in rdt_mon_features_show to hide bmec related feature.
> 
> v13: New patch to hide BMEC related files.
> ---
>  fs/resctrl/rdtgroup.c | 42 +++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 41 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
> index 92bb8f3adfae..8c67e0897f25 100644
> --- a/fs/resctrl/rdtgroup.c
> +++ b/fs/resctrl/rdtgroup.c
> @@ -1164,7 +1164,8 @@ static int rdt_mon_features_show(struct kernfs_open_file *of,
>  		if (mevt->rid != r->rid || !mevt->enabled)
>  			continue;
>  		seq_printf(seq, "%s\n", mevt->name);
> -		if (mevt->configurable)
> +		if (mevt->configurable &&
> +		    !resctrl_arch_mbm_cntr_assign_enabled(r))
>  			seq_printf(seq, "%s_config\n", mevt->name);
>  	}
>  
> @@ -1813,6 +1814,38 @@ static ssize_t mbm_local_bytes_config_write(struct kernfs_open_file *of,
>  	return ret ?: nbytes;
>  }
>  
> +/**
> + * resctrl_bmec_files_show() — Controls the visibility of BMEC-related resctrl
> + * files. When @show is true, the files are displayed; when false, the files
> + * are hidden.
> + */
> +static void resctrl_bmec_files_show(struct rdt_resource *r, bool show)
> +{
> +	struct kernfs_node *kn_config, *l3_mon_kn;
> +	char name[32];
> +
> +	sprintf(name, "%s_MON", r->name);
> +	l3_mon_kn = kernfs_find_and_get(kn_info, name);

Similar to comment about resctrl_mkdir_counter_configs() (resctrl_mkdir_event_configs())
I think this can be avoided by calling resctrl_bmec_files_show() from 
rdtgroup_mkdir_info_resdir().

> +	if (!l3_mon_kn)
> +		return;
> +
> +	kn_config = kernfs_find_and_get(l3_mon_kn, "mbm_total_bytes_config");
> +	if (kn_config) {
> +		kernfs_get(kn_config);

Be careful ... kernfs_find_and_get() already took a reference. Additional
kernfs_get() is not needed.

> +		kernfs_show(kn_config, show);
> +		kernfs_put(kn_config);
> +	}
> +
> +	kn_config = kernfs_find_and_get(l3_mon_kn, "mbm_local_bytes_config");
> +	if (kn_config) {
> +		kernfs_get(kn_config);
> +		kernfs_show(kn_config, show);
> +		kernfs_put(kn_config);
> +	}
> +
> +	kernfs_put(l3_mon_kn);
> +}
> +
>  static int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
>  					struct seq_file *s, void *v)
>  {
> @@ -2808,6 +2841,13 @@ static int rdtgroup_create_info_dir(struct kernfs_node *parent_kn)
>  			ret = resctrl_mkdir_counter_configs(r, name);
>  			if (ret)
>  				goto out_destroy;
> +
> +			/*
> +			 * Hide BMEC related files if mbm_event mode
> +			 * is enabled.
> +			 */
> +			if (resctrl_arch_mbm_cntr_assign_enabled(r))
> +				resctrl_bmec_files_show(r, false);
>  		}
>  	}
>  

Reinette