linux-kernel - Re: [PATCH v8 07/21] x86/resctrl: Add end-marker to the resctrl_event

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Message-ID: <fcbb5285-2d78-4181-8ee5-977382a36cde@arm.com>
Date: Thu, 24 Apr 2025 10:15:41 +0100
From: James Morse <james.morse@....com>
To: "Luck, Tony" <tony.luck@...el.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
 Reinette Chatre <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>,
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 D Scott Phillips OS <scott@...amperecomputing.com>,
 carl@...amperecomputing.com, lcherian@...vell.com,
 bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
 baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
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 Shaopeng Tan <tan.shaopeng@...fujitsu.com>
Subject: Re: [PATCH v8 07/21] x86/resctrl: Add end-marker to the
 resctrl_event_id enum

Hi Tony,

On 15/04/2025 19:56, Luck, Tony wrote:
> On Fri, Apr 11, 2025 at 04:42:15PM +0000, James Morse wrote:
>> The resctrl_event_id enum gives names to the counter event numbers on x86.
>> These are used directly by resctrl.
>>
>> To allow the MPAM driver to keep an array of these the size of the enum
>> needs to be known.
>>
>> Add a 'num_events' define which can be used to size an array. This isn't
>> a member of the enum to avoid updating switch statements that would
>> otherwise be missing a case.
> 
> I'm adding more events in this series:
> 
> https://lore.kernel.org/all/20250407234032.241215-1-tony.luck@intel.com/
> 
> Any switches in existing code would need to have a "default:" case

Boo. I much prefer the no-default case as it forces someone adding a new enum entry
to inspect every switch statement. But I'll change it.


> added because the new events are in the same "enum" but totally
> unrelated to the existing events. Other code changes in that series
> deleted many of the switches anyway.

Cool!


> Patch 23 in that series changes QOS_NUM_EVENTS from a #define
> to the last element in the enum without any issues.

I'll do that here and add the defaults in this patch to reduce conflicts.


Thanks,

James