linux-kernel - Re: [PATCH v21 09/18] x86/resctrl: Add a new field to struct rmid

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Date: Tue, 25 Jun 2024 16:29:22 -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 v21 09/18] x86/resctrl: Add a new field to struct
 rmid_read for summation of domains

Hi Tony,

On 6/21/24 3:38 PM, Tony Luck wrote:
> When a user reads a monitor file rdtgroup_mondata_show() calls
> mon_event_read() to package up all the required details into an rmid_read
> structure which is passed across the smp_call*() infrastructure to code
> that will read data from hardware and return the value (or error status)
> in the rmid_read structure.
> 
> Sub-NUMA Cluster (SNC) mode adds files with new semantics. These require
> the smp_call-ed code to sum event data from all domains that share an
> L3 cache.
> 
> Add a pointer to the L3 "cacheinfo" structure to struct rmid_read
> for the data collection routines to use to pick the domains to be
> summed.
> 
> Reinette suggested that the rmid_read structure has become complex enough
> to warrant documentation of each of its fields and provided the kerneldoc
> documentation for struct rmid_read.
> 
> Co-developed-by: Reinette Chatre <reinette.chatre@...el.com>
> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>   arch/x86/kernel/cpu/resctrl/internal.h | 19 +++++++++++++++++++
>   1 file changed, 19 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 135190e0711c..d04018b8b571 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -144,12 +144,31 @@ union mon_data_bits {
>   	} u;
>   };
>   
> +/**
> + * struct rmid_read - Data passed across smp_call*() to read event count.
> + * @rgrp:  Resource group for which the counter is being read. If it is a parent
> + *	   resource group then its event count is summed with the count from all
> + *	   its child resource groups.
> + * @r:	   Resource describing the properties of the event being read.
> + * @d:	   Domain that the counter should be read from. If NULL then sum all
> + *	   domains in @r sharing L3 @ci.id
> + * @evtid: Which monitor event to read.
> + * @first: Initialize MBM counter when true.
> + * @ci:    Cacheinfo for L3. Only set when @d is NULL. Used when summing domains.
> + * @err:   Error encountered when reading counter.
> + * @val:   Returned value of event counter. If @rgrp is a parent resource group,
> + *	   @val contains the sum of event counts from its child resource groups.

(nit: "contains" -> "includes" [1] to indicate sum is from parent as well as children)

Reinette

[1] https://lore.kernel.org/lkml/2e083f94-d982-412f-b212-1d520d7743c5@intel.com/