linux-kernel - Re: [PATCH v18 12/17] x86/resctrl: Create Sub-NUMA (SNC) monitor files

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Date: Wed, 22 May 2024 14:19:48 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>, Maciej
 Wieczor-Retman <maciej.wieczor-retman@...el.com>, Peter Newman
	<peternewman@...gle.com>, James Morse <james.morse@....com>, Babu Moger
	<babu.moger@....com>, Drew Fustini <dfustini@...libre.com>, Dave Martin
	<Dave.Martin@....com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v18 12/17] x86/resctrl: Create Sub-NUMA (SNC) monitor
 files

Hi Tony,

On 5/15/2024 3:23 PM, Tony Luck wrote:
> When SNC mode is enabled, create subdirectories and file to monitor

"and file" -> "and files"?

> at the SNC node granularity. Monitor files at the L3 granularity are
> tagged with a "sum" attribute to indicate that all SNC nodes sharing
> an L3 cache should be read and summed to provide the result to the
> user.

Why go through effort to create a generic "monitor display scope" and
then just always refer to it as L3 cache scope? One consequence is that
the code and changelog seems to have a disconnect.

> 
> Note that the "domid" field for files that must sum across SNC domains
> has the L3 cache instance id, while non-summing files use the domain id.
> 
> Also the "sum" files do not need to make a call to mon_event_read() to
> initialize the MBM counters. This will be handled by initializing the
> individual SNC nodes that share the L3.
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 53 ++++++++++++++++++--------
>  1 file changed, 38 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 7a6c40aefdcc..f0f468babdea 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -3026,7 +3026,8 @@ static void rmdir_mondata_subdir_allrdtgrp(struct rdt_resource *r,
>  }
>  
>  static int mon_add_all_files(struct kernfs_node *kn, struct rdt_mon_domain *d,
> -			     struct rdt_resource *r, struct rdtgroup *prgrp)
> +			     struct rdt_resource *r, struct rdtgroup *prgrp,
> +			     bool do_sum)
>  {
>  	union mon_data_bits priv;
>  	struct mon_evt *mevt;
> @@ -3037,15 +3038,18 @@ static int mon_add_all_files(struct kernfs_node *kn, struct rdt_mon_domain *d,
>  		return -EPERM;
>  
>  	priv.u.rid = r->rid;
> -	priv.u.domid = d->hdr.id;
> +	priv.u.domid = do_sum ? d->display_id : d->hdr.id;
> +	priv.u.sum = do_sum;
>  	list_for_each_entry(mevt, &r->evt_list, list) {
>  		priv.u.evtid = mevt->evtid;
>  		ret = mon_addfile(kn, mevt->name, priv.priv);
>  		if (ret)
>  			return ret;
>  
> -		if (is_mbm_event(mevt->evtid))
> +		if (!do_sum && is_mbm_event(mevt->evtid)) {
> +			rr.sumdomains = 0;
>  			mon_event_read(&rr, r, d, prgrp, mevt->evtid, true);
> +		}
>  	}
>  
>  	return 0;
> @@ -3055,23 +3059,42 @@ static int mkdir_mondata_subdir(struct kernfs_node *parent_kn,
>  				struct rdt_mon_domain *d,
>  				struct rdt_resource *r, struct rdtgroup *prgrp)
>  {
> -	struct kernfs_node *kn;
> +	struct kernfs_node *kn, *ckn;
>  	char name[32];
> +	bool do_sum;
>  	int ret;
>  
> -	sprintf(name, "mon_%s_%02d", r->name, d->hdr.id);
> -	/* create the directory */
> -	kn = kernfs_create_dir(parent_kn, name, parent_kn->mode, prgrp);
> -	if (IS_ERR(kn))
> -		return PTR_ERR(kn);
> +	do_sum = r->mon_scope != r->mon_display_scope;
> +	sprintf(name, "mon_%s_%02d", r->name, d->display_id);

Why not just determine "display_id" dynamically here and pass it as parameter
to mon_add_all_files()? Previously you mentioned that error handling is a problem
but this flow can surely handle errors, no?

> +	kn = kernfs_find_and_get_ns(parent_kn, name, NULL);
> +	if (!kn) {
> +		/* create the directory */
> +		kn = kernfs_create_dir(parent_kn, name, parent_kn->mode, prgrp);
> +		if (IS_ERR(kn))
> +			return PTR_ERR(kn);
>  
> -	ret = rdtgroup_kn_set_ugid(kn);
> -	if (ret)
> -		goto out_destroy;
> +		ret = rdtgroup_kn_set_ugid(kn);
> +		if (ret)
> +			goto out_destroy;
> +		ret = mon_add_all_files(kn, d, r, prgrp, do_sum);
> +		if (ret)
> +			goto out_destroy;
> +	}
>  
> -	ret = mon_add_all_files(kn, d, r, prgrp);
> -	if (ret)
> -		goto out_destroy;
> +	if (do_sum) {
> +		sprintf(name, "mon_sub_%s_%02d", r->name, d->hdr.id);
> +		ckn = kernfs_create_dir(kn, name, parent_kn->mode, prgrp);
> +		if (IS_ERR(ckn))
> +			goto out_destroy;
> +
> +		ret = rdtgroup_kn_set_ugid(ckn);
> +		if (ret)
> +			goto out_destroy;
> +
> +		ret = mon_add_all_files(ckn, d, r, prgrp, false);
> +		if (ret)
> +			goto out_destroy;
> +	}
>  
>  	kernfs_activate(kn);
>  	return 0;

Reinette