linux-kernel - Re: RE: [PATCH v8 08/21] x86/resctrl: Expand the width of dom_id by replacing mon_data

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Message-ID: <93da0002-a326-49f2-af5d-f89da9d3a8f6@amd.com>
Date: Tue, 22 Apr 2025 12:59:31 -0500
From: "Moger, Babu" <bmoger@....com>
To: "Luck, Tony" <tony.luck@...el.com>, James Morse <james.morse@....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>,
 Babu Moger <Babu.Moger@....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>,
 "fenghuay@...dia.com" <fenghuay@...dia.com>
Subject: Re: RE: [PATCH v8 08/21] x86/resctrl: Expand the width of dom_id by
 replacing mon_data_bits

Hi Tony,

On 4/22/2025 12:14 PM, Luck, Tony wrote:
>> Do we really need to maintain a separate list for all the private pointers?
>>
>> Here's my understanding of the patch—please correct me if I’m missing
>> anything:
>>
>> Patch Requirements:
>>
>> 1. Expand dom_id.
>>
>> 2. Pack all necessary data (dom_id, event_id, resid) into the
>> of->kn->priv pointer when creating event files in the mon_data
>> directory for each domain.
> 
> This step includes searching the list of previously created priv structures
> to find a matching one that can be shared.  This happens all the time
> because the same set of values is re-used over and over. Essentially
> we only allocate anything while creating the mon_data directory in the
> root directory of resctrl. James' original implementation made use of
> this by special case allocation for the default group, and then doing
> kernfs lookups while creating new groups to find the matching one
> and linking to the same ->priv pointer.
> 

oh ok.

I went back and looked at the history.
https://lore.kernel.org/all/20250228195913.24895-38-james.morse@arm.com/

So you are saying, kernfs lookup method is much more complex. So, having 
the global list is easy to traverse and efficient?

Thanks
Babu