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

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Date: Thu, 7 Mar 2024 09:41:33 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: "Luck, Tony" <tony.luck@...el.com>, "Wieczor-Retman, Maciej"
	<maciej.wieczor-retman@...el.com>
CC: "Yu, Fenghua" <fenghua.yu@...el.com>, Shuah Khan <shuah@...nel.org>,
	"james.morse@....com" <james.morse@....com>, "ilpo.jarvinen@...ux.intel.com"
	<ilpo.jarvinen@...ux.intel.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-kselftest@...r.kernel.org"
	<linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH 4/4] selftests/resctrl: Adjust SNC support messages

Hi Tony,

On 3/7/2024 9:18 AM, Luck, Tony wrote:
>>> If so, what should it be named? "snc_ways" as a kernel variable was
>>> later replaced by "snc_nodes_per_l3_cache". Is that a good filename?
>>
>> "snc_nodes_per_l3_cache" seems okay to me.
>>
>> And I understand that the file content would show SNC mode and the presence or
>> absence of this file would tell if kernel supports SNC?
> 
> Yes. The existence of the file indicates the kernel is SNC aware.
> 
> The value read from the file would give the number of nodes per L3 (obviously :-) )
> 
> SNC not supported by this platform or not enabled:
> 
> $ cat /sys/fs/resctrl/info/L3_mon/ snc_nodes_per_l3_cache
> 1
> 
> SNC2 enabled:
> 
> $ cat /sys/fs/resctrl/info/L3_mon/ snc_nodes_per_l3_cache
> 2
> 

This would be useful. I believe "SNC" is architecture specific?
What if the file always exists and is named "nodes_per_l3_cache"?

I assume that the internals of handling more nodes per L3 cache should
be hidden from user space and it should not be necessary for user space
to know if this is because of SNC or potentially some other mechanism on
another platform?

I think that may reduce fragmentation of resctrl .... not having
resctrl look so different on different architectures but maintains
the promise of a generic interface.

I am not sure if this is specific to monitoring though,
why not host file in /sys/fs/resctrl/info/L3 ? 

Reinette