linux-kernel - Re: [PATCH v18 11/17] x86/resctrl: Allocate a new bit in union mon_data

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Message-ID: <7764b46c-85e7-4d5a-947d-87cf51c27bb2@intel.com>
Date: Wed, 22 May 2024 14:16:48 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>,
	"Maciej Wieczor-Retman" <maciej.wieczor-retman@...el.com>, Peter Newman
	<peternewman@...gle.com>, James Morse <james.morse@....com>, Babu Moger
	<babu.moger@....com>, Drew Fustini <dfustini@...libre.com>, Dave Martin
	<Dave.Martin@....com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v18 11/17] x86/resctrl: Allocate a new bit in union
 mon_data_bits

Hi Tony,

On 5/15/2024 3:23 PM, Tony Luck wrote:
> When Sub-NUMA (SNC) mode is enabled the legacy monitor reporting files

Sub-NUMA Cluster (SNC)? (I'll stop pointing these out.)

> must report the sum of the data from all of the SNC nodes that share the
> L3 cache that is referenced by the monitor file.
> 
> Resctrl squeezes all the attributes of these files into 32-bits so they
> can be stored in the "priv" field of struct kernfs_node.
> 
> Steal one bit from the "evtid" field (currently 8 bits, but only three
> events supported by Intel) to create a new "sum" field that indicates

This is filesystem code so should surely not be just about what us supported
by Intel.

> this file must sum across SNC nodes. This bit also indicates that the
> domid field is the display_id to match to find which domains must be
> summed.
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  arch/x86/kernel/cpu/resctrl/internal.h | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 498c5d240c68..c54ad12ff2b8 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -132,14 +132,19 @@ struct mon_evt {
>   *                     as kernfs private data
>   * @rid:               Resource id associated with the event file
>   * @evtid:             Event id associated with the event file
> - * @domid:             The domain to which the event file belongs
> + * @sum:               Set when event must be summed across multiple
> + *                     domains.
> + * @domid:             When @sum is zero this is the domain to which
> + *                     the event file belongs. When sum is one this

sum -> @sum to be consistent with previous sentence?

> + *                     is the display_id of all domains to be summed

"is the monitoring display scope id shared with other monitoring
domains to be summed"?

>   * @u:                 Name of the bit fields struct
>   */
>  union mon_data_bits {
>  	void *priv;
>  	struct {
>  		unsigned int rid		: 10;
> -		enum resctrl_event_id evtid	: 8;
> +		enum resctrl_event_id evtid	: 7;
> +		unsigned int sum		: 1;
>  		unsigned int domid		: 14;
>  	} u;
>  };

Reinette