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

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Message-ID: <Z1eEti6Kswtb3HC5@agluck-desk3>
Date: Mon, 9 Dec 2024 16:00:54 -0800
From: "Luck, Tony" <tony.luck@...el.com>
To: Reinette Chatre <reinette.chatre@...el.com>
Cc: Borislav Petkov <bp@...en8.de>, "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

On Mon, Dec 09, 2024 at 03:40:12PM -0800, Reinette Chatre wrote:
> 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 is right. The post-split home of this is not <linux/resctrl.h>
but fs/resctrl/internal.h which doesn't exist yet.

So Boris is right, this declaration should be added to arch/x86/kernel/cpu/resctrl/internal.h
by this patch to be moved later.

> 
> [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/

-Tony