linux-kernel - Re: [PATCH v11 2/8] x86/resctrl: Prepare for per-CTRL_MON group mba

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Message-ID: <678cef69-78ef-4951-bd31-10abe646e6d8@intel.com>
Date: Mon, 9 Dec 2024 15:40:12 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: "Luck, Tony" <tony.luck@...el.com>, Borislav Petkov <bp@...en8.de>
CC: "Yu, Fenghua" <fenghua.yu@...el.com>, Peter Newman
	<peternewman@...gle.com>, Jonathan Corbet <corbet@....net>, "x86@...nel.org"
	<x86@...nel.org>, James Morse <james.morse@....com>, Jamie Iles
	<quic_jiles@...cinc.com>, Babu Moger <babu.moger@....com>, Randy Dunlap
	<rdunlap@...radead.org>, "Shaopeng Tan (Fujitsu)" <tan.shaopeng@...itsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: Re: [PATCH v11 2/8] x86/resctrl: Prepare for per-CTRL_MON group
 mba_MBps control

Hi Tony,

On 12/9/24 2:35 PM, Luck, Tony wrote:
>>> mba_mbps_default_event isn't architecture specific. The mba_MBps
>>> feedback code could be implemented on any architecture that supports
>>> both measurement and control of memory bandwidth.
>>
>> Yes, and it should be moved to that header then, right?
>>
>> But not earlier.
> 
> If you feel strongly about it then go ahead and cut the line from <linux/rectrl.h>
> and paste it into <asm/resctrl.h>

I am not sure about this ... I expect the code needing this initially will
form part of the filesystem code so it may be more intuitive to have it
be located in arch/x86/kernel/cpu/resctrl/internal.h as Boris suggested.
As part of the arch/fs split it may then move to fs/resctrl/internal.h

mba_mbps_default_event may even stay internal to the fs/resctrl code with an
arch helper created later to initialize it. This is because I think
the initialization of mba_mbps_default_event may move out of
get_rdt_mon_resources() into resctrl_mon_resource_init() that is being
created as part of the MPAM work [1]. An example of current fs initialization
done in arch code that is moved to it can be found in [2].

Reinette

[1] https://lore.kernel.org/all/20241004180347.19985-17-james.morse@arm.com/
[2] https://lore.kernel.org/all/20241004180347.19985-20-james.morse@arm.com/