linux-kernel - Re: [PATCH v15-RFC 0/8] Add support for Sub-NUMA cluster (SNC) systems

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Date: Mon, 12 Feb 2024 14:05:10 -0800
From: Tony Luck <tony.luck@...el.com>
To: Reinette Chatre <reinette.chatre@...el.com>
Cc: "babu.moger@....com" <babu.moger@....com>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Peter Newman <peternewman@...gle.com>,
	Jonathan Corbet <corbet@....net>,
	Shuah Khan <skhan@...uxfoundation.org>,
	"x86@...nel.org" <x86@...nel.org>,
	Shaopeng Tan <tan.shaopeng@...itsu.com>,
	James Morse <james.morse@....com>,
	Jamie Iles <quic_jiles@...cinc.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Drew Fustini <dfustini@...libre.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: Re: [PATCH v15-RFC 0/8] Add support for Sub-NUMA cluster (SNC)
 systems

On Mon, Feb 12, 2024 at 01:43:56PM -0800, Reinette Chatre wrote:
> Hi Tony,
> 
> On 2/12/2024 11:57 AM, Luck, Tony wrote:
> >>> To be honest, I like this series more than the previous series. I always
> >>> thought RDT_RESOURCE_L3_MON should have been a separate resource by itself.
> >>
> >> Would you prefer that your "Reviewed-by" tag be removed from the
> >> previous series?
> > 
> > I'm thinking that I could continue splitting things and break "struct rdt_resource" into
> > separate "ctrl" and "mon" structures. Then we'd have a clean split from top to bottom.
> 
> It is not obvious what you mean with "continue splitting things". Are you
> speaking about "continue splitting from v14" or "continue splitting from v15-RFC"?

I'm speaking of some future potential changes. Not proposing to
do this now.

> I think that any solution needs to consider what makes sense for resctrl
> as a whole instead of how to support SNC with smallest patch possible.

I am officially abandoning my v15-RFC patches. I wasn't clear enough in
my e-mail earlier today.

https://lore.kernel.org/all/SJ1PR11MB608378D1304224D9E8A9016FFC482@SJ1PR11MB6083.namprd11.prod.outlook.com/
> 
> There should not be any changes that makes resctrl harder to understand
> and maintain, as exemplified by confusion introduced by a simple thing as
> resource name choice [1].
> 
> > 
> > Doing that would get rid of the rdt_resources_all[] array. Replacing with individual
> > rdt_hw_ctrl_resource and rdt_hw_mon_resource declarations for each feature.
> >
> > Features found on a system would be added to a list of ctrl or list of mon resources.
> 
> Could you please elaborate what is architecturally wrong with v14 and how this
> new proposal addresses that?

There is nothing architecturally wrong with v14. I thought it was more
complex than it needed to be. You have convinced me that my v15-RFC
series, while simpler, is not a reasonable path for long-term resctrl
maintainability.
> 
> Reinette
> 
> [1] https://lore.kernel.org/lkml/ZcZyqs5hnQqZ5ZV0@agluck-desk3/

-Tony