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Message-ID: <0463b814-f304-6317-f3c1-226688f33f8b@arm.com>
Date: Mon, 22 Jan 2024 18:05:32 +0000
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Subject: Re: [PATCH v8 06/24] x86/resctrl: Access per-rmid structures by index
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To: Reinette Chatre <reinette.chatre@intel.com>, x86@kernel.org,
 linux-kernel@vger.kernel.org
Cc: Fenghua Yu <fenghua.yu@intel.com>, Thomas Gleixner <tglx@linutronix.de>,
 Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
 H Peter Anvin <hpa@zytor.com>, Babu Moger <Babu.Moger@amd.com>,
 shameerali.kolothum.thodi@huawei.com,
 D Scott Phillips OS <scott@os.amperecomputing.com>,
 carl@os.amperecomputing.com, lcherian@marvell.com,
 bobo.shaobowang@huawei.com, tan.shaopeng@fujitsu.com,
 baolin.wang@linux.alibaba.com, Jamie Iles <quic_jiles@quicinc.com>,
 Xin Hao <xhao@linux.alibaba.com>, peternewman@google.com,
 dfustini@baylibre.com, amitsinght@marvell.com
References: <20231215174343.13872-1-james.morse@arm.com>
 <20231215174343.13872-7-james.morse@arm.com>
 <0072e1fe-7c4e-4bd2-a1d9-24c2161d14d6@intel.com>
From: James Morse <james.morse@arm.com>
In-Reply-To: <0072e1fe-7c4e-4bd2-a1d9-24c2161d14d6@intel.com>
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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@intel.com>

Thanks!

James