linux-kernel - Re: [PATCH v19 00/20] Add support for Sub-NUMA cluster (SNC) systems

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Date: Wed, 29 May 2024 19:46:27 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>
CC: 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>,
	<x86@...nel.org>, <linux-kernel@...r.kernel.org>, <patches@...ts.linux.dev>
Subject: Re: [PATCH v19 00/20] Add support for Sub-NUMA cluster (SNC) systems

Hi Tony,

On 5/29/24 1:20 PM, Tony Luck wrote:
> On Tue, May 28, 2024 at 03:55:29PM -0700, Reinette Chatre wrote:
>> Hi Tony,
>>> 13:	Wordsmith commit into imperative.
>>> 	I looked at using kobject_has_children() to check for empty
>>> 	directory, but it needs a "struct kobject *" and all I have
>>> 	is "struct kernfs_node *". I'm now checking how many CPUs
>>
>> Consider how kobject_has_children() uses that struct kobject *.
>> Specifically:
>> 	return kobj->sd && kobj->sd->dir.subdirs
>>
>> It operates on kobj->sd, which is exactly what you have: struct kernfs_node.
> 
> So right. My turn to grumble about other peoples choice of names. If
> that field was named "kn" instead of "sd" I would have spotted this
> too.
> 
>>> 	remain in ci->shared_cpu_map to detect whether this is the
>>> 	last SNC node.
>>
>> hmmm, ok, will take a look ... but please finalize discussion of a patch series
>> before submitting a new series that rejects feedback without discussion and
>> does something completely different in new version.
> 
> Reinette,
> 
> So here's what rmdir_mondata_subdir_allrdtgrp() looks like using the
> subdirs check. It might need an update/better header comment.
> 
> -Tony
> 
> ---
> 
> /*
>   * Remove all subdirectories of mon_data of ctrl_mon groups
>   * and monitor groups with given domain id.

(note comment still considers that domain id is parameter)

>   */
> static void rmdir_mondata_subdir_allrdtgrp(struct rdt_resource *r,
> 					   struct rdt_mon_domain *d)
> {
> 	struct rdtgroup *prgrp, *crgrp;
> 	struct kernfs_node *kn;
> 	char subname[32];

I wonder if static checkers will know that this cannot be used
uninitialized?

> 	char name[32];
> 
> 	sprintf(name, "mon_%s_%02d", r->name, d->ci->id);
> 	if (r->mon_scope != RESCTRL_L3_CACHE) {
> 		/*
> 		 * SNC mode: Unless the last domain is being removed must
> 		 * just remove the SNC subdomain.
> 		 */
> 		sprintf(subname, "mon_sub_%s_%02d", r->name, d->hdr.id);
> 	}
> 
> 	list_for_each_entry(prgrp, &rdt_all_groups, rdtgroup_list) {
> 		kn = kernfs_find_and_get(prgrp->mon.mon_data_kn, name);
> 		if (!kn)
> 			continue;
> 
> 		if (kn->dir.subdirs <= 1)
> 			kernfs_remove(kn);
> 		else
> 			kernfs_remove_by_name(kn, subname);
> 
> 		list_for_each_entry(crgrp, &prgrp->mon.crdtgrp_list, mon.crdtgrp_list) {
> 			kn = kernfs_find_and_get(crgrp->mon.mon_data_kn, name);
> 			if (!kn)
> 				continue;
> 
> 			if (kn->dir.subdirs <= 1)
> 				kernfs_remove(kn);
> 			else
> 				kernfs_remove_by_name(kn, subname);
> 		}
> 	}
> }

This solution looks more intuitive to me. I do think that it may be
missing some kernfs_put()'s?

Reinette

ps. Please do give me a couple of days more with this series before you
     submit a new version.