linux-kernel - Re: [PATCH v5 24/29] x86/resctrl: Add energy/perf choices to rdt boot option

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Message-ID: <aEYGCUuKS8_MDorA@agluck-desk3>
Date: Sun, 8 Jun 2025 14:52:09 -0700
From: "Luck, Tony" <tony.luck@...el.com>
To: Fenghua Yu <fenghuay@...dia.com>
Cc: Reinette Chatre <reinette.chatre@...el.com>,
	Maciej Wieczor-Retman <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>,
	Anil Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	Chen Yu <yu.c.chen@...el.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH v5 24/29] x86/resctrl: Add energy/perf choices to rdt
 boot option

On Fri, Jun 06, 2025 at 04:55:37PM -0700, Fenghua Yu wrote:
> Hi, Tony,
> 
> On 5/21/25 15:50, Tony Luck wrote:
> > Users may want to force either of the telemetry features on
> > (in the case where they are disabled due to erratum) or off
> > (in the case that a limited number of RMIDs for a telemetry
> > feature reduces the number of monitor groups that can be
> > created.)

[SNIP]

> > diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> > index f07f5b58639a..b23309566500 100644
> > --- a/arch/x86/kernel/cpu/resctrl/core.c
> > +++ b/arch/x86/kernel/cpu/resctrl/core.c
> > @@ -797,6 +797,8 @@ enum {
> >   	RDT_FLAG_MBA,
> >   	RDT_FLAG_SMBA,
> >   	RDT_FLAG_BMEC,
> > +	RDT_FLAG_ENERGY,
> > +	RDT_FLAG_PERF,
> >   };
> >   #define RDT_OPT(idx, n, f)	\
> > @@ -822,6 +824,8 @@ static struct rdt_options rdt_options[]  __ro_after_init = {
> >   	RDT_OPT(RDT_FLAG_MBA,	    "mba",	X86_FEATURE_MBA),
> >   	RDT_OPT(RDT_FLAG_SMBA,	    "smba",	X86_FEATURE_SMBA),
> >   	RDT_OPT(RDT_FLAG_BMEC,	    "bmec",	X86_FEATURE_BMEC),
> > +	RDT_OPT(RDT_FLAG_ENERGY,    "energy",	0),
> > +	RDT_OPT(RDT_FLAG_PERF,	    "perf",	0),
> 
> Boot options "energy" and "perf" are PMT event groups level. Other boot
> options are individual event level.
> 
> E.g. "!perf" forces off all 7 PMT PERF events.
> 
> e.g. "uops retired" event has an erratum but all other PERF events work
> fine. Disabling "perf" group disables all PERF events. Is "!perf" a useful
> boot option?
> 
> Is there any consideration to have boot options at PMT event group level
> instead of individual PMT event level like legacy events?

This could be done. But it would add some complexity that may never
be needed. I'm optimisitic that all events in a group will work.

> 
> [SNIP]
> 
> Thanks.
> 
> -Fenghua
>