linux-kernel - Re: [PATCH] x86/resctrl: Don't try to free nonexistent RMIDs

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Message-ID: <d476585b-3cfb-494d-b25c-4aeb6244e21d@intel.com>
Date: Tue, 18 Jun 2024 08:43:51 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Dave Martin <Dave.Martin@....com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>, James Morse
	<james.morse@....com>, Fenghua Yu <fenghua.yu@...el.com>, Thomas Gleixner
	<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
	<bp@...en8.de>, H Peter Anvin <hpa@...or.com>, Babu Moger
	<Babu.Moger@....com>, <shameerali.kolothum.thodi@...wei.com>, "D Scott
 Phillips OS" <scott@...amperecomputing.com>, <carl@...amperecomputing.com>,
	<lcherian@...vell.com>, <bobo.shaobowang@...wei.com>, "Shaopeng Tan
 (Fujitsu)" <tan.shaopeng@...itsu.com>, <baolin.wang@...ux.alibaba.com>, Jamie
 Iles <quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>, Peter Newman
	<peternewman@...gle.com>, <dfustini@...libre.com>, <amitsinght@...vell.com>,
	David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>
Subject: Re: [PATCH] x86/resctrl: Don't try to free nonexistent RMIDs

Hi Dave,

On 6/18/24 2:30 AM, Dave Martin wrote:
> On Mon, Jun 17, 2024 at 08:53:38AM -0700, Reinette Chatre wrote:
>> On 6/17/24 4:55 AM, Dave Martin wrote:

>>> As it happens I tested with rdt=cmt,mbmtotal,mbmlocal,l3cat,l3cdp
>>> (though I made no effort to exercise these features other than running
>>> the selftests).  I can note this in the commit if you prefer.
>>
>> hmmm ... those parameters should not be necessary unless the system
>> has those features forced off by default because of errata. Doing
>> functional testing on these systems via such enabling is fine
>> though.
>>
>> Reinette
> 
> I got these kernel args from James.  Apparently some of these features
> are defaulted to off by the firmware on the box I'm using, but we're not
> sure why.  I haven't dug into it.

resctrl does not provide capability to override features that the hardware
does not advertise as supporting. resctrl does sometimes force hardware
advertised features off because of errata (for example, see [1]) and the
kernel "rdt=" parameter can be used to override that. This same option also
enables administrators to ignore some features on their platforms.

Reinette

[1] https://lore.kernel.org/all/3aea0a3bae219062c812668bd9b7b8f1a25003ba.1503512900.git.tony.luck@intel.com/