linux-kernel - RE: [PATCH v6 36/42] x86/resctrl: Add end-marker to the resctrl_event

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Message-ID: <SJ1PR11MB6083221B0AACE9A732EED878FCCC2@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Fri, 28 Feb 2025 20:59:09 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: James Morse <james.morse@....com>, "babu.moger@....com"
	<babu.moger@....com>, "x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: "Chatre, Reinette" <reinette.chatre@...el.com>, Thomas Gleixner
	<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
	<bp@...en8.de>, H Peter Anvin <hpa@...or.com>,
	"shameerali.kolothum.thodi@...wei.com"
	<shameerali.kolothum.thodi@...wei.com>, D Scott Phillips OS
	<scott@...amperecomputing.com>, "carl@...amperecomputing.com"
	<carl@...amperecomputing.com>, "lcherian@...vell.com" <lcherian@...vell.com>,
	"bobo.shaobowang@...wei.com" <bobo.shaobowang@...wei.com>,
	"tan.shaopeng@...itsu.com" <tan.shaopeng@...itsu.com>,
	"baolin.wang@...ux.alibaba.com" <baolin.wang@...ux.alibaba.com>, Jamie Iles
	<quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>,
	"peternewman@...gle.com" <peternewman@...gle.com>, "dfustini@...libre.com"
	<dfustini@...libre.com>, "amitsinght@...vell.com" <amitsinght@...vell.com>,
	David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>, Dave
 Martin <dave.martin@....com>, "Ko, Koba" <kobak@...dia.com>, "Shanker
 Donthineni" <sdonthineni@...dia.com>, Shaopeng Tan
	<tan.shaopeng@...fujitsu.com>
Subject: RE: [PATCH v6 36/42] x86/resctrl: Add end-marker to the
 resctrl_event_id enum

> >> @@ -51,4 +51,6 @@ enum resctrl_event_id {
> >>    QOS_L3_MBM_LOCAL_EVENT_ID       = 0x03,
> >>  };
> >>
> >> +#define QOS_NUM_EVENTS            (QOS_L3_MBM_LOCAL_EVENT_ID + 1)
>
> > Why cant this be part of "enum resctrl_event_id" like we defined
> > RDT_NUM_RESOURCES?
>
> Maybe its a difference that only exists in my head, but the rdt resource array is
> completely a resctrl concept, the positions in the enum don't mean anything.
> Not so for for resctrl_event_id - those numbers mean something to the X86 CPUs. Resctrl
> needs some unique identifier for those, and its simpler just to use these directly. I
> didn't want to add anything to this enum.
>
> If there are mpam specific events, (currently there is only the risk of bandwidth counters
> on the L2, or scattered at random through the system), I'd prefer to support them via perf
> and keep them out of here completely.

Also note that resctrl code has some "switch (evtid) {" code ... if you make QOS_NUM_EVENTS
a member of the enum, then the compiler will warn if you don't have a "default:" or a
"case QOS_NUM_EVENTS:" to cover all the options.

We don't have any "switch (r->rid)"

-Tony