linux-kernel - Re: [PATCH v6 08/22] x86/resctrl: Introduce interface to display number of monitoring counters

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Message-ID: <6c1305ae-caa3-4da1-a0c2-3948cac976be@intel.com>
Date: Fri, 16 Aug 2024 14:34:04 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <fenghua.yu@...el.com>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <paulmck@...nel.org>,
	<rdunlap@...radead.org>, <tj@...nel.org>, <peterz@...radead.org>,
	<yanjiewtw@...il.com>, <kim.phillips@....com>, <lukas.bulwahn@...il.com>,
	<seanjc@...gle.com>, <jmattson@...gle.com>, <leitao@...ian.org>,
	<jpoimboe@...nel.org>, <rick.p.edgecombe@...el.com>,
	<kirill.shutemov@...ux.intel.com>, <jithu.joseph@...el.com>,
	<kai.huang@...el.com>, <kan.liang@...ux.intel.com>,
	<daniel.sneddon@...ux.intel.com>, <pbonzini@...hat.com>,
	<sandipan.das@....com>, <ilpo.jarvinen@...ux.intel.com>,
	<peternewman@...gle.com>, <maciej.wieczor-retman@...el.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<eranian@...gle.com>, <james.morse@....com>
Subject: Re: [PATCH v6 08/22] x86/resctrl: Introduce interface to display
 number of monitoring counters

Hi Babu,

On 8/6/24 3:00 PM, Babu Moger wrote:
> The ABMC feature provides an option to the user to assign a hardware

Here and in all patches, when referring to resctrl fs please use the more
generic "mbm_assign_cntr" mode to distinguish it from the hardware/architecture
specific code that involves ABMC. Something like

"The ABMC feature provides" -> ""mbm_cntr_assign" mode provides"

I also think that being explicit with this separation will help us to see
gaps in interface between resctrl fs and arch.

> counter to an RMID and monitor the bandwidth as long as the counter is

Please clarify the scope of this feature. Above mentions that a counter is
assigned to an RMID but later it is mentioned that the counter is assigned
to an event. Perhaps consistently mention that a counter is assigned to
a RMID,event pair?

> assigned. Number of assignments depend on number of monitoring counters
> available.
> 
> Provide the interface to display the number of monitoring counters
> supported.
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
> v6: No changes.
> 
> v5: Changed the display name from num_cntrs to num_mbm_cntrs.
>      Updated the commit message.
>      Moved the patch after mbm_mode is introduced.
> 
> v4: Changed the counter name to num_cntrs. And few text changes.
> 
> v3: Changed the field name to mbm_assign_cntrs.
> 
> v2: Changed the field name to mbm_assignable_counters from abmc_counte
> ---
>   Documentation/arch/x86/resctrl.rst     |  3 +++
>   arch/x86/kernel/cpu/resctrl/monitor.c  |  2 ++
>   arch/x86/kernel/cpu/resctrl/rdtgroup.c | 16 ++++++++++++++++
>   3 files changed, 21 insertions(+)
> 
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index d4ec605b200a..fe9f10766c4f 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -291,6 +291,9 @@ with the following files:
>   		as long as there are enough RMID counters available to support number
>   		of monitoring groups.
>   
> +"num_mbm_cntrs":
> +	The number of monitoring counters available for assignment.
> +
>   "max_threshold_occupancy":
>   		Read/write file provides the largest value (in
>   		bytes) at which a previously used LLC_occupancy
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 5e8706ab6361..83329cefebf7 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -1242,6 +1242,8 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
>   			r->mon.num_mbm_cntrs = (ebx & 0xFFFF) + 1;
>   			if (WARN_ON(r->mon.num_mbm_cntrs > 64))
>   				r->mon.num_mbm_cntrs = 64;
> +
> +			resctrl_file_fflags_init("num_mbm_cntrs", RFTYPE_MON_INFO);

The arch code should not access the resctrl file flags. This should be moved to make
the MPAM support easier. With the arch code setting r->mon.mbm_cntr_assignable the
fs code can use that to set the flags. Something similar to below patch is needed:
https://lore.kernel.org/lkml/20240802172853.22529-27-james.morse@arm.com/

>   		}
>   	}
>   

Reinette