linux-kernel - Re: [PATCH] fs/resctrl,x86/resctrl: Factor mba rounding to be per-arch

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Message-ID: <883591c4-6301-45f6-a671-ca55974aaac0@intel.com>
Date: Sun, 12 Oct 2025 01:15:07 +0800
From: "Chen, Yu C" <yu.c.chen@...el.com>
To: Reinette Chatre <reinette.chatre@...el.com>, Dave Martin
	<Dave.Martin@....com>
CC: "Luck, Tony" <tony.luck@...el.com>, <linux-kernel@...r.kernel.org>, "James
 Morse" <james.morse@....com>, Thomas Gleixner <tglx@...utronix.de>, "Ingo
 Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
	<dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, "Jonathan
 Corbet" <corbet@....net>, <x86@...nel.org>, <linux-doc@...r.kernel.org>
Subject: Re: [PATCH] fs/resctrl,x86/resctrl: Factor mba rounding to be
 per-arch

On 10/11/2025 12:48 AM, Reinette Chatre wrote:
> Hi Dave,
> 
> On 9/30/25 8:40 AM, Dave Martin wrote:
>> On Mon, Sep 29, 2025 at 09:09:35AM -0700, Reinette Chatre wrote:
>>> On 9/29/25 6:56 AM, Dave Martin wrote:
>>>> On Thu, Sep 25, 2025 at 03:58:35PM -0700, Luck, Tony wrote:
>>>>> On Mon, Sep 22, 2025 at 04:04:40PM +0100, Dave Martin wrote:

[snip]

>> Anyway, going back to the "#" convention:
>>
>> If the initial read of schemata has the new entries "pre-commented",
>> then userspace wouldn't need to know about the new entries.  It could
>> just tweak the MB entry (which it knows about), and write the file back:
>>
>> 	MB: 0=43
>> 	# MB_HW: 0=2
>> 	# MB_MIN: 0=1
>> 	# MB_MAX: 0=2
>>
>> then resctrl knows to ignore the hashed lines, and so reading the file
>> back gives:
>>
>> 	MB: 0=43
>> 	# MB_HW: 0=3
>> 	# MB_MIN: 0=2
>> 	# MB_MAX: 0=3


May I ask if introducing the pre-commented lines is intended to prevent
control conflicts over the same MBA? If this is the case, I wonder if,
instead of exposing both MB and the pre-commented MB_HW_X in one file,
it would be  feasible to introduce a new mount option (such as "hw") to
  make the legacy MB and MB_HW_X mutually exclusive. If the user specifies
  "hw" in mount option, display MB_HW_X (if available); otherwise, display
only the legacy "MB". This is similar to the cpufreq governor, where only
one governor is allowed to adjust the CPU frequency at a time.

thanks,
Chenyu