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

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Date: Tue, 18 Jun 2024 17:16:48 +0100
From: Dave Martin <Dave.Martin@....com>
To: Reinette Chatre <reinette.chatre@...el.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 Reinette,

On Tue, Jun 18, 2024 at 08:43:51AM -0700, Reinette Chatre wrote:
> 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/

Possibly the box in question falls under this case.  I'll need to check
with James and/or experiment.

Either way, I don't think this impacts the tested-ness of this patch,
but please shout if you have concerns.

Cheers
---Dave