linux-kernel - Re: [PATCH v8 06/24] x86/resctrl: Access per-rmid structures by index

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Date: Fri, 15 Dec 2023 20:58:16 -0800
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>, D Scott Phillips OS
	<scott@...amperecomputing.com>, <carl@...amperecomputing.com>,
	<lcherian@...vell.com>, <bobo.shaobowang@...wei.com>,
	<tan.shaopeng@...itsu.com>, <baolin.wang@...ux.alibaba.com>, Jamie Iles
	<quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>,
	<peternewman@...gle.com>, <dfustini@...libre.com>, <amitsinght@...vell.com>
Subject: Re: [PATCH v8 06/24] x86/resctrl: Access per-rmid structures by index

Hi James,

On 12/15/2023 9:43 AM, James Morse wrote:
> x86 systems identify traffic using the CLOSID and RMID. The CLOSID is
> used to lookup the control policy, the RMID is used for monitoring. For
> x86 these are independent numbers.
> Arm's MPAM has equivalent features PARTID and PMG, where the PARTID is
> used to lookup the control policy. The PMG in contrast is a small number
> of bits that are used to subdivide PARTID when monitoring. The
> cache-occupancy monitors require the PARTID to be specified when
> monitoring.
> 
> This means MPAM's PMG field is not unique. There are multiple PMG-0, one
> per allocated CLOSID/PARTID. If PMG is treated as equivalent to RMID, it
> cannot be allocated as an independent number. Bitmaps like rmid_busy_llc
> need to be sized by the number of unique entries for this resource.
> 
> Treat the combined CLOSID and RMID as an index, and provide architecture
> helpers to pack and unpack an index. This makes the MPAM values unique.
> The domain's rmid_busy_llc and rmid_ptrs[] are then sized by index, as
> are domain mbm_local[] and mbm_total[].
> 
> x86 can ignore the CLOSID field when packing and unpacking an index, and
> report as many indexes as RMID.
> 
> Signed-off-by: James Morse <james.morse@....com>
> Tested-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Tested-by: Peter Newman <peternewman@...gle.com>
> Tested-by: Babu Moger <babu.moger@....com>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Reviewed-by: Babu Moger <babu.moger@....com>
> ---

Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>

Reinette