linux-kernel - RE: [PATCH v8 08/25] x86/resctrl: Introduce interface to display number of monitoring counters

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Message-ID: <SJ1PR11MB6083583A24FA3B3B7C2DCD64FC442@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Mon, 14 Oct 2024 19:51:48 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: "babu.moger@....com" <babu.moger@....com>, "Chatre, Reinette"
	<reinette.chatre@...el.com>
CC: "corbet@....net" <corbet@....net>, "Yu, Fenghua" <fenghua.yu@...el.com>,
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	"tj@...nel.org" <tj@...nel.org>, "peterz@...radead.org"
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 Rick P" <rick.p.edgecombe@...el.com>, "kirill.shutemov@...ux.intel.com"
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	"peternewman@...gle.com" <peternewman@...gle.com>, "Wieczor-Retman, Maciej"
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	<linux-kernel@...r.kernel.org>, "Eranian, Stephane" <eranian@...gle.com>,
	"james.morse@....com" <james.morse@....com>
Subject: RE: [PATCH v8 08/25] x86/resctrl: Introduce interface to display
 number of monitoring counters

> > What advantage does it have over skipping the per-domain list and
> > just providing a single value for all domains? You clearly expect this
> > will be a common user request since you implemented the "*" means
> > apply to all domains.
> >
>
> We started with a global assignment by applying assignment across all the
> domains initially.
>
> But we wanted give a generic approach which allows both the options(domain
> specific assignment and global assignment with '*"). It is also matches
> with other managements (RMID/CLOSID management) we are doing in resctrl
> right now. Also, there is an extra IPI for each domain if user is only
> interested in on domain.
>
> Some of the discussions are here.
> https://lore.kernel.org/lkml/f7dac996d87b4144e4c786178a7fd3d218eaebe8.1711674410.git.babu.moger@amd.com/#r

My summary of that:

Peter: Complex, don't need per-domain.
Reinette: Maybe some architecture might want per-domain.

Since you seem to want to keep the flexibility for a possible future
where per-domain is needed. The "available_mbm_cntrs" file
suggested in another thread would need to list available counters
on each domain to avoid ABI problems should that future arrive.

$ cat num_mbm_counters
32

$ cat available_mbm_cntrs
0=12;1=9

Current implementation would show same number for all domains.

-Tony