linux-kernel - RE: [PATCH v18 06/17] x86/resctrl: Introduce snc_nodes_per_l3

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Date: Thu, 23 May 2024 21:25:41 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: "Chatre, Reinette" <reinette.chatre@...el.com>, "Yu, Fenghua"
	<fenghua.yu@...el.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>
CC: "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 v18 06/17] x86/resctrl: Introduce snc_nodes_per_l3_cache

> > I'm also contemplating dropping snc_nodes_per_l3_cache from being a
> > global variable and making it a field in "struct rdt_resource" (only needed
> > for the RDT_RESOURCE_L3 resource). N.B. Babu had suggested it
> > shouldn't be global many patch versions ago.
> >
> > Perhaps name it .domains_per_l3_cache or .subdomains_per_l3_cache?
> >
> > Bad idea? Good idea (but you have a better name for the field)?
>
> With the check in supports_mba_mbps() changed I do not see
> snc_nodes_per_l3_cache needed by anything but arch specific code.
> I thus do not see any reason for the resctrl filesystem (or, for
> example, Arm) to know that this value even exists.
>
> While struct rdt_hw_resource is a place to put architecture
> specific information it does not seem appropriate to force every
> resource to carry what is essentially a system wide (not specific to
> resctrl) L3 specific property. To me this really seems like an
> architecture specific global setting but I'd also like to hear the
> motivations why it should not be.

So (in arch/x86/kernel/cpu/resctrl/monitor.c)

static int snc_nodes_per_l3_cache = 1;

Set and use only in this (arch specific) file.

-Tony