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

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Date: Mon, 22 Jan 2024 18:05:32 +0000
From: James Morse <james.morse@....com>
To: Reinette Chatre <reinette.chatre@...el.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 Reinette,

On 16/12/2023 04:58, Reinette Chatre wrote:
> 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.

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

Thanks!

James