linux-kernel - Re: [PATCH v6 07/42] x86/resctrl: Add max_bw to struct resctrl

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Message-ID: <b487ae9b-99b5-40b6-a6c5-a90ab62baa5e@intel.com>
Date: Wed, 19 Feb 2025 14:14:29 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: James Morse <james.morse@....com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, H Peter Anvin <hpa@...or.com>, Babu Moger
	<Babu.Moger@....com>, <shameerali.kolothum.thodi@...wei.com>, "D Scott
 Phillips OS" <scott@...amperecomputing.com>, <carl@...amperecomputing.com>,
	<lcherian@...vell.com>, <bobo.shaobowang@...wei.com>,
	<tan.shaopeng@...itsu.com>, <baolin.wang@...ux.alibaba.com>, Jamie Iles
	<quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>,
	<peternewman@...gle.com>, <dfustini@...libre.com>, <amitsinght@...vell.com>,
	David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>,
	"Dave Martin" <dave.martin@....com>, Koba Ko <kobak@...dia.com>, Shanker
 Donthineni <sdonthineni@...dia.com>, Shaopeng Tan
	<tan.shaopeng@...fujitsu.com>, "Tony Luck" <tony.luck@...el.com>
Subject: Re: [PATCH v6 07/42] x86/resctrl: Add max_bw to struct resctrl_membw

Hi James,

On 2/7/25 10:17 AM, James Morse wrote:
> __rdt_get_mem_config_amd() and __get_mem_config_intel() both use
> the default_ctrl property as a maximum value. This is because the
> MBA schema works differently between these platforms. Doing this
> complicates determining whether the default_ctrl property belongs
> to the arch code, or can be derived from the schema format.
> 
> Deriving the maximum or default value from the schema format would
> avoid the architecture code having to tell resctrl such obvious
> things as the maximum percentage is 100, and the maximum bitmap
> is all ones.
> 
> Maximum bandwidth is always going to vary per platform. Add
> max_bw as a special case. This is currently used for the maximum
> MBA percentage on Intel platforms, but can be removed from the
> architecture code if 'percentage' becomes a schema format resctrl
> supports directly.
> 
> This value isn't needed for other schema formats.
> 
> This will allow the default_ctrl to be generated from the schema
> properties when it is needed.
> 
> Signed-off-by: James Morse <james.morse@....com>
> Tested-by: Carl Worth <carl@...amperecomputing.com> # arm64
> Tested-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> ---

Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>

Reinette