linux-kernel - Re: [PATCH v3 45/47] arm_mpam: Add workaround for T241-MPAM-4

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Message-ID: <e38cb392-ff29-4008-aa4f-e9d7166836f0@arm.com>
Date: Mon, 19 Jan 2026 20:56:17 +0000
From: Ben Horgan <ben.horgan@....com>
To: Fenghua Yu <fenghuay@...dia.com>
Cc: amitsinght@...vell.com, baisheng.gao@...soc.com,
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Subject: Re: [PATCH v3 45/47] arm_mpam: Add workaround for T241-MPAM-4

Hi Fenghua,

On 1/15/26 23:20, Fenghua Yu wrote:
> Hi, Shanker and Ben,
> 
> On 1/12/26 08:59, Ben Horgan wrote:
>> From: Shanker Donthineni <sdonthineni@...dia.com>
>>
>> In the T241 implementation of memory-bandwidth partitioning, in the
>> absence
>> of contention for bandwidth, the minimum bandwidth setting can affect the
>> amount of achieved bandwidth. Specifically, the achieved bandwidth in the
>> absence of contention can settle to any value between the values of
>> MPAMCFG_MBW_MIN and MPAMCFG_MBW_MAX.  Also, if MPAMCFG_MBW_MIN is set
>> zero (below 0.78125%), once a core enters a throttled state, it will
>> never
>> leave that state.
>>
>> The first issue is not a concern if the MPAM software allows to program
>> MPAMCFG_MBW_MIN through the sysfs interface. This patch ensures program
>> MBW_MIN=1 (0.78125%) whenever MPAMCFG_MBW_MIN=0 is programmed.
> 
> When MBW_MIN=1, min mem bw can be very low when contention. This may
> drop mem access performance. Is it possible to set MBW_MIN bigger so
> that ensure the floor of mem access is high?

Isn't that a policy decision rather than something we should be putting
in a quirk framework?

Thanks,

Ben