linux-kernel - Re: [PATCH 2/2] x86/resctrl: Fix memory bandwidth counter width for Hygon

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Message-ID: <6a77f0dd-ea2a-4e2c-bf16-a3d660399051@open-hieco.net>
Date: Sun, 7 Dec 2025 10:26:57 +0800
From: Xiaochen Shen <shenxiaochen@...n-hieco.net>
To: "Luck, Tony" <tony.luck@...el.com>,
 "Chatre, Reinette" <reinette.chatre@...el.com>, "bp@...en8.de"
 <bp@...en8.de>, "fenghuay@...dia.com" <fenghuay@...dia.com>
Cc: "babu.moger@....com" <babu.moger@....com>,
 "james.morse@....com" <james.morse@....com>,
 "Dave.Martin@....com" <Dave.Martin@....com>, "x86@...nel.org"
 <x86@...nel.org>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>, shenxiaochen@...n-hieco.net
Subject: Re: [PATCH 2/2] x86/resctrl: Fix memory bandwidth counter width for
 Hygon

Hi Tony,

On 12/7/2025 12:14 AM, Xiaochen Shen wrote:
>> Question: What is the value of "hw_res->mon_scale" on a Hygon system?
> I have double confirmed with Hygon hardware architect, in the testing Hygon system:
> hw_res->mon_scale: 64
> hw_res->mbm_width: 32
> 
> Here is a rough calculation for the theoretical max bandwidth by the hardware counter:
> (1) 32-bits width and mon_scale is 64:
> 2 ^32 * 64 = 2 ^38 = 256 (B/s)
> 

Sorry. Here is a typo:
- 2 ^32 * 64 = 2 ^38 = 256 (B/s)
+ 2 ^32 * 64 = 2 ^38 = 256G (B/s) 


> (2) 24-bits width and mon_scale is 64 (this is highly likely to cause overflow):
> 2 ^24 * 64 = 2 ^30 = 1G (B/s)


Best regards,
Xiaochen Shen