linux-kernel - Re: [PATCH 0/1] fs/resctrl: Show domain CPU list in schema output

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Message-ID: <c26dierez6gzngp2syreufhdwhx64iuiox6cqrpeomz2ieuwkh@4l35mbkc4ez6>
Date: Fri, 31 Oct 2025 17:25:41 -0400
From: Aaron Tomlin <atomlin@...mlin.com>
To: "Luck, Tony" <tony.luck@...el.com>
Cc: "Chatre, Reinette" <reinette.chatre@...el.com>, 
	"Dave.Martin@....com" <Dave.Martin@....com>, "james.morse@....com" <james.morse@....com>, 
	"babu.moger@....com" <babu.moger@....com>, "tglx@...utronix.de" <tglx@...utronix.de>, 
	"mingo@...hat.com" <mingo@...hat.com>, "bp@...en8.de" <bp@...en8.de>, 
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	atomlin@...mlin.com
Subject: Re: [PATCH 0/1] fs/resctrl: Show domain CPU list in schema output

On Fri, Oct 31, 2025 at 07:03:15PM +0000, Luck, Tony wrote:
> 1) You'd also need to change the "write" path for the schemata file
> (treating the CPU list as read-only).
> 
> 2) This would break user ABI, so is not going to happen.

Hi Tony,

Thank you for following up.

If I understand correctly, parse_cbm() and parse_bw() would return -EINVAL
if the user incorrectly included the CPU list, no?

I suspect the issue is if one can read something from a file, one should be
able to write the same thing back and have it either succeed or process
only the valid parts. I agree maintaining ABI compatibility while allowing
the new verbose output on the read path is not ideal.

> Users can see the association between the domain numbers and
> CPUs in sysfs.
> 
> $ cat /sys/devices/system/cpu/cpu0/cache/index3/id
> 0
> $ cat /sys/devices/system/cpu/cpu0/cache/index3/shared_cpu_list
> 0-27
> 
> Maybe not as convenient as a direct read-out in the schemata file.
> But the information is easily accessible.

No, using the above to establish the association is absolutely fine. 


Kind regards,

-- 
Aaron Tomlin