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

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Date: Tue, 18 Jun 2024 10:30:07 +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,

On Mon, Jun 17, 2024 at 08:53:38AM -0700, Reinette Chatre wrote:
> Hi Dave,
> 
> On 6/17/24 4:55 AM, Dave Martin wrote:
> > Hi Reinette,
> > 
> > On Fri, Jun 14, 2024 at 03:47:58PM -0700, Reinette Chatre wrote:
> > > Hi Dave,
> > > 
> > > On 6/14/24 9:08 AM, Dave Martin wrote:
> > > > Commit 6791e0ea3071 ("x86/resctrl: Access per-rmid structures by
> > > > index") adds logic to map individual monitoring groups into a
> > > > global index space used for tracking allocated RMIDs.
> > > > 
> > > > That patch keept the logic to ignore requests to free the default
> > > 
> > > keept -> kept
> > > 
> > > nitpick: I actually do not know if "that patch" gets same hate as
> > > "this patch" so to avoid any potential feedback about this I'd like
> > > to suggest that this is rewritten without this term. Perhaps
> > > something like: "Requests to free the default RMID in free_rmid()
> > > are ignored, and this works fine on x86."
> > > 
> > > > RMID in free_rmid(), and this works fine on x86.
> > > > 
> > 
> > How about recasting the first paragraph into the past tense (since it
> > relates a past commit), and rewording as "Requests to free the default
> > RMID continued to be ignored in free_rmid(), and this works fine on
> > x86."
> 
> Please keep it in the present tense. I do not see this as relating to
> a "past commit" but instead it is an existing commit responsible for
> current behavior. Documentation/process/maintainer-tip.rst contains
> some example changelogs created by x86 maintainers that captures their
> requirements. The beginning "context" portion is always in present
> tense.

Fair enough.  I'll reword this as per your suggestion.

[...]

> > > > Tested on x86 (But so far for the monitors-present case.
> > > 
> > > Tested by booting with "rdt=!cmt,!mbmtotal,!mbmlocal".
> > 
> > Thanks (I take it that's your test, not a request to be more specific
> > about mine?)
> 
> Yes, I did test it with those parameters. You are also welcome to
> add:
> Tested-by: Reinette Chatre <reinette.chatre@...el.com>

Ah, right.  Thanks.

> > 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.

Cheers
---Dave