linux-kernel - Re: [PATCH v4 06/19] x86/resctrl: Introduce interface to display number of ABMC counters

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Date: Thu, 13 Jun 2024 17:57:51 -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 v4 06/19] x86/resctrl: Introduce interface to display
 number of ABMC counters

Hi Babu,

On 5/24/24 5:23 AM, Babu Moger wrote:
> The ABMC feature provides an option to the user to assign a hardware
> counter to an RMID and monitor the bandwidth as long as the counter
> is assigned. Number of assignments depend on number of ABMC counters
> available.

Take care that this interface will not just be used by ABMC. I assumed that
when the user switches to "soft-RMID" then the value of "num_cntrs" will change?

> 
> Provide the interface to display the number of ABMC counters supported.
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
> 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_counters.
> ---
>   Documentation/arch/x86/resctrl.rst     |  4 ++++
>   arch/x86/kernel/cpu/resctrl/monitor.c  |  1 +
>   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 02790efaabcc..7ab8172ef208 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -257,6 +257,10 @@ with the following files:
>   	    # cat /sys/fs/resctrl/info/L3_MON/mbm_local_bytes_config
>   	    0=0x30;1=0x30;3=0x15;4=0x15
>   
> +"num_cntrs":
> +	Available when ABMC feature is supported. The number of ABMC counters
> +	available for configuration.

This can only be understood by folks already familiar with AMD's ABMC feature. There is
no information about what "ABMC feature" is, what an "ABMC counter" is and what
"configuration" can be done with it.

Do you think this num_cntrs will only be used by ABMC? What will happen when user
enables "soft-RMID" or some other mode?

Reinette