linux-kernel - Re: [PATCH v5 08/40] x86/resctrl: Generate default

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Message-ID: <3780be3c-07d9-4c36-a1aa-eae505ce8cb0@intel.com>
Date: Wed, 23 Oct 2024 14:15:39 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: James Morse <james.morse@....com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>
CC: Fenghua Yu <fenghua.yu@...el.com>, 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>, Shaopeng Tan
	<tan.shaopeng@...fujitsu.com>
Subject: Re: [PATCH v5 08/40] x86/resctrl: Generate default_ctrl instead of
 sharing it

Hi James,

On 10/4/24 11:03 AM, James Morse wrote:
> The struct rdt_resource default_ctrl is used by both the architecture
> code for resetting the hardware controls, and by the filesystem parts
> of resctrl to report to user-space.

This is not accurate. The hardware controls may be different from
what is reported to user-space, for example when MBA software controller
is active.

> 
> This means the value has to be shared, but might not match the
> properties of the control. e.g. a percentage greater than 100.

Are you referring to software controller here? When would this not
match properties of control? That this value may not match properties
of control contradicts first paragraph that this is used to reset the
control ...

> 
> Instead, determine the default control value from a shared helper
> resctrl_get_default_ctrl() that uses the schema properties to
> determine the correct value.
> 
> 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>
> ---

Reinette