linux-kernel - Re: [PATCH v2 07/24] x86/resctrl: Store the effective num

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Date:   Wed, 31 Mar 2021 14:39:11 -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,
        Jamie Iles <jamie@...iainc.com>,
        D Scott Phillips OS <scott@...amperecomputing.com>
Subject: Re: [PATCH v2 07/24] x86/resctrl: Store the effective num_closid in
 the schema

Hi James,

On 3/12/2021 9:58 AM, James Morse wrote:
> The resctrl_schema struct holds properties that vary with the style of
> configuration that resctrl applies to a resource.
> 
> There are already two values for the hardware's num_closid, depending on
> whether the architecture presents the L3 or L3CODE/L3DATA resources.
> 
> As the way CDP changes the number of control groups that resctrl can create
> is part of the user-space interface, it should be managed by the filesystem

s/create is part of/create as part of/ ?

> parts of resctrl. This allows the architecture code to only describe the
> value the hardware supports.
> 
> Add num_closid to resctrl_schema. This is the value seen by the filesystem,
> and when the CDP resources are merged, will be different to the value
> described by the arch code when CDP is enabled.
> 
> These functions operate on the num_closid value that is exposed to
> user-space:
> rdtgroup_parse_resource()
> rdtgroup_schemata_show()
> rdt_num_closids_show()
> closid_init()
> 
> These are changed to use the schema value instead.
> 
> schemata_list_create() sets this value, and reaches into the architecture
> specific structure to get the value. This will eventually be replaced with
> a helper.
> 
> Reviewed-by: Jamie Iles <jamie@...iainc.com>
> Signed-off-by: James Morse <james.morse@....com>


...

> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index c6f749f54765..0ff10468940b 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -165,10 +165,12 @@ struct rdt_resource {
>    * @list:	Member of resctrl's schema list
>    * @conf_type:	Whether this entry is for code/data/both
>    * @res:	The rdt_resource for this entry
> + * @num_closid:	Number of CLOSIDs available for this resource

It is not clear what "this resource" is. This description is essentially 
the same as its copy found in rdt_hw_resource. Could you please improve 
these descriptions to capture the differences between the two num_closid 
values?

Thank you

Reinette