linux-kernel - Re: [PATCH v11 20/31] fs/resctrl: Refactor Sub-NUMA Cluster (SNC) in mkdir/rmdir code flow

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Message-ID: <aOf0yA1AWlzJLf8H@agluck-desk3>
Date: Thu, 9 Oct 2025 10:45:44 -0700
From: "Luck, Tony" <tony.luck@...el.com>
To: Reinette Chatre <reinette.chatre@...el.com>
CC: Fenghua Yu <fenghuay@...dia.com>, "Wieczor-Retman, Maciej"
	<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>, "Chen,
 Yu C" <yu.c.chen@...el.com>, "x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: Re: [PATCH v11 20/31] fs/resctrl: Refactor Sub-NUMA Cluster (SNC) in
 mkdir/rmdir code flow

On Wed, Oct 08, 2025 at 07:16:07PM -0700, Reinette Chatre wrote:
> Understood. This is not about correctness but making the code easier to understand.
> What I am aiming for is consistency in the code where the pattern
> in existing flows use the resource ID as check to direct code flow to resource
> specific code. In the above flow it uses the monitoring scope. This works of course,
> but it is an implicit check because the L3 resource is the only one that currently
> supports the "node" scope and does so when SNC is enabled. 
> My preference is for the code to be consistent in patterns used and find doing so
> makes the code easier to read and understand.
> 
Reinette,

Should I address this "only one that currently" issue now? Maybe by
adding a bool "rdt_resource:snc_mode" so the implicit

	if (r->mon_scope == RESCTRL_L3_NODE)

changes to:

	if (r->snc_mode)

There are only two places where SNC mode is checked in this way. The
others rely on seeing that mon_data::sum is set, or that rr->hdr is
NULL. So it seems like a very small improvement.

If we ever add a node scoped resource that isn't related to SNC, it
would be needed at that point. But I'm not sure why hardware would
ever do that.

-Tony