linux-kernel - Re: [PATCH 1/2] x86/resctrl: Add io_alloc_min_cbm

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Message-ID: <knqdzael7yihvznsdzijztawviex2n3i5pqbzslmk3rolnacrh@h3cwjthvyeuz>
Date: Mon, 10 Nov 2025 19:41:28 -0500
From: Aaron Tomlin <atomlin@...mlin.com>
To: Babu Moger <bmoger@....com>
Cc: tony.luck@...el.com, reinette.chatre@...el.com, Dave.Martin@....com, 
	james.morse@....com, babu.moger@....com, tglx@...utronix.de, mingo@...hat.com, 
	bp@...en8.de, dave.hansen@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86/resctrl: Add io_alloc_min_cbm_all interface for
 CBM reset

On Mon, Nov 10, 2025 at 10:34:48AM -0600, Babu Moger wrote:
> Does the following option work for you?
> 
> # echo "*=0" > /sys/fs/resctrl/info/L3/io_alloc_cbm
> 
> 
> Here,|*| represents all domains.

Hi Babu,

Thank you for your response.

Unfortunately, this approach will not work.

If I understand correctly, the assumption that echo 0 (which translates to
a CBM of all zeros) would always be accepted as a "minimum" value is
incorrect since r->cache.min_cbm_bits could be greater than zero
(e.g., under Intel hardware). See rdt_init_res_defs_intel().

The goal is not just to "clear" the CBM, but to reset it to the smallest
valid mask.

Kind regards,
-- 
Aaron Tomlin