Re: [PATCH 4/4] selftests/resctrl: Adjust SNC support messages

From: Reinette Chatre <reinette.chatre@intel.com>
To: "Luck, Tony" <tony.luck@intel.com>, James Morse <james.morse@arm.com>
Cc: "Wieczor-Retman, Maciej" <maciej.wieczor-retman@intel.com>,
	"Yu, Fenghua" <fenghua.yu@intel.com>,
	Shuah Khan <shuah@kernel.org>,
	"ilpo.jarvinen@linux.intel.com" <ilpo.jarvinen@linux.intel.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-kselftest@vger.kernel.org"
	<linux-kselftest@vger.kernel.org>
Subject: Re: [PATCH 4/4] selftests/resctrl: Adjust SNC support messages
Date: Mon, 18 Mar 2024 14:23:13 -0700	[thread overview]
Message-ID: <fe4a54cf-7103-49c7-add4-ee4bcf76c7b3@intel.com> (raw)
In-Reply-To: <SJ1PR11MB608303C5E0BEB42CAC5B02BAFC2D2@SJ1PR11MB6083.namprd11.prod.outlook.com>

Hi Tony,

On 3/18/2024 1:47 PM, Luck, Tony wrote:
>> What is the use case for needing to expose the individual cluster counts? What if
>> resctrl just summed the cluster counts and presented the data as before - per L3
>> cache instance? I doubt that resctrl would be what applications would use to verify
>> whether they are "well behaved" wrt NUMA.
> 
> Reinette,
> 
> My (perhaps naïve) belief is that in a cloud server environment there are many
> well behaved NUMA applications. Only presenting the sum would lose the detailed
> information from each SNC node.

Yes ...  I understand by providing a sum the values that contributed to the sum
are lost.

Could you please help me understand the details by answering my first
question: What is the use case for needing to expose the individual cluster
counts? 

This is a model specific feature so if this is something needed for just a
couple of systems I think we should be less inclined to make changes to
resctrl interface. I am starting to be concerned about something similar
becoming architectural later and then we need to wrangle this model specific
resctrl support (which has then become ABI) again to support whatever that
may look like.

Reinette