linux-kernel - Re: [PATCH v9 6/9] x86/resctrl: Add "mba_MBps_event" file to ctrl

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Message-ID: <4796ded1-a988-4038-bdbb-fc9a93da0c55@intel.com>
Date: Tue, 19 Nov 2024 20:03:06 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>, "Peter
 Newman" <peternewman@...gle.com>, Jonathan Corbet <corbet@....net>,
	<x86@...nel.org>
CC: 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-doc@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v9 6/9] x86/resctrl: Add "mba_MBps_event" file to ctrl_mon
 directories

Hi Tony,

On 11/13/24 4:17 PM, Tony Luck wrote:
> The "mba_MBps" mount option provides an alternate method to
> control memory bandwidth. Instead of specifying allowable
> bandwidth as a percentage of maximum possible, the user
> provides a MiB/s limit value.
> 
> Historically the limit was enforced by a feedback loop from

"Historically the limit was enforced" no history needed since
this is still the case at the time of this patch.

> the measure local bandwidth to adjust the memory bandwidth
> allocation controls.

I am not sure what is meant by "a feedback loop from the measure
local bandwidth" (that was copy&pasted to next patch).

> 
> In preparation to allow the user to pick the memory bandwidth
> monitoring event used as input to the feedback loop, provide
> a file in each ctrl_mon group directory that shows the event

In the documentation the custom is to use CTRL_MON.

> currently in use.

Much better changelog. I think it will help to add a snippet that
mentions the file is only visible to user space if resctrl
was mounted with mba_MBps, and thus only visible when mba_sc is
enabled, and thus reinforcing that this maintains the contract
that rdtgrp->mba_mbps_event is only accessed when mba_sc is enabled.

> 
> Suggested-by: Reinette Chatre <reinette.chatre@...el.com>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---

Reinette