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

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Message-ID: <99e33a39-f0ec-488b-88d9-634158aec6e1@intel.com>
Date: Fri, 5 Dec 2025 13:57:41 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: Xiaochen Shen <shenxiaochen@...n-hieco.net>, "Luck, Tony"
	<tony.luck@...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>
Subject: Re: [PATCH 2/2] x86/resctrl: Fix memory bandwidth counter width for
 Hygon

Hi Xiaochen,

On 12/4/25 6:38 PM, Xiaochen Shen wrote:
> Hi Tony,
> 
> On 12/5/2025 1:11 AM, Luck, Tony wrote:
>> I *think* you'd get the right results if the h/w counter is wider
>> than s/w expects. You'd just need to keep polling fast enough
>> (and we never adjusted the MBM polling rate from the original
>> 1 HZ.)
> 
> Thank you very much for code review!
> 
> We have observed a test case where an incorrect counter width leads to random unexpected memory bandwidth readings:
> https://github.com/shenxiaochen/my_documents/blob/main/memory_bandwidth_counter_width_and_overflow_issue_steps_to_reproduce.txt

Could this perhaps be related to issue fixed by:
15292f1b4c55 ("x86/resctrl: Fix miscount of bandwidth event when reactivating previously unavailable RMID")?

Reinette